The Greatest PC Mysteries--Solved!

PC owners know that every computer has a unique assortment of components, applications and peripherals. Nevertheless, certain things--including a host of common PC problems and mysteries--are part of the shared experience of computer ownership. The editors at PCWorld have seen and solved hundreds of PC mysteries, ranging from balky printers to diffident video players to persnickety file attachments. Most of the answers to these tech questions are simple and straightforward, so we've taken the liberty of compiling some of the most frequently encountered PC mysteries into a single list that we'll update regularly. Following each question we provide a short response that summarizes what we know. For a more detailed explanation and some helpful tips, click the links in each answer.

Why is [Program X] always running when I start my PC?

Windows maintains a list of programs that automatically run every time you boot up your computer. Some of these startup programs (such as antivirus utilities) are beneficial, but many of them are not necessary and can slow your PC as they run automatically in the background. Speed up your boot time by disabling Windows startup programs.

Why does my PC keep making a grinding sound?

This can happen for a lot of reasons--and unfortunately almost all of them are bad news. The most likely answer is that a fan or hard drive in your PC is starting to die, causing it to spin off-kilter. PCWorld contributing editor Lincoln Spector wrote a smart guide to pinpointing the source of a grinding-sound problem in this Answer Line column. No matter what the cause turns out to be, you should immediately back up your hard drive, just in case.

Grinding sounds usually mean trouble, but backing up your data to an external drive can mitigate the damage.

Why do I need administrator access to delete certain files?

That requirement is just a security precaution: Windows 7 insists that you have administrator access in order to modify or delete files when doing so might affect other people who use the computer. If you need to delete something and you don't have the password to get into the administrator account (if you bought the PC used, for example) here's how to gain administrator access without a password.

Why did Windows come bundled with so many unwanted programs?

For once, Microsoft isn't to blame. Most PC manufacturers stuff new computers with extraneous trial versions of games, movie players, antivirus utilities, and other software. If you want to get rid of this bloatware, here's how to remove preinstalled software from your PC.

Why won't Windows allow me to delete a certain file?

If Windows refuses to delete a file or folder, some application or process is accessing it; you must close that application before you can finish deleting the unwanted file.

Why does Windows sometimes reboot without my permission, and how do I prevent that from happening?

This problem relates to how Windows installs automatic updates. Fortunately, you can make adjust some settings to put yourself back in control.

I updated my hardware drivers and now my PC is acting funny. What happened?

Though it's a good idea to download the latest drivers for your components, occasionally a buggy or beta driver update may degrade your PC's performance. If that happens, try to roll back to a previous version of the driver that you know is safe; if you can't do that, you'll have to uninstall the problematic driver entirely. Our walkthrough of how to uninstall drivers in Windows explains how to perform a rollback and how to uninstall a driver.

Does it matter whether I 'safely remove' devices?

Absolutely: If you ignore Windows' requests to "safely remove" your storage media, you could end up with corrupted files, un­­readable media, or both.

Where did my downloaded files go? Why can't I find them?

Your browser chooses where downloads go, but you can control the process.

Why are some of my critical files hidden?

Windows typically keeps critical system files hidden from view to make it more difficult for untrained users to modify or delete them, and thereby inadvertently cause a system error. Usually the only hidden files are ones you shouldn't tamper with (such as your boot.ini file); however, if you need to find a file or folder and you think it might be hidden, check out our tips on how to view hidden files and file extensions in Windows.

Why doesn't my iPad charge when I connect it to my computer?

Your PC's USB port doesn't supply enough juice to charge a new iPad quickly--but you can still charge your iPad gradually. Some USB ports, however, like the ones highlighted in red below, have a higher trickle charge rate to help you charge smartphones, tablets, and other external devices.

If your PC has red USB ports, they sport increased power output and should be used to charge your iPad or other USB-powered devices.

Why does a video play on my desktop but not my laptop?

If a computer doesn't have the specific decoder required for a video format, you can't watch the video. Make sure that you get the right one.

My printer won't print, and Windows won't let me cancel or delete print jobs. What's going on?

Usually this problem arises because of a communication problem between the PC and the printer. When they have trouble talking to each other, you may need to help them.

I hear beeps when I turn on my PC. What do they mean?

Those beeps come from the BIOS (a piece of software built into the motherboard). Specific "beep codes" have specific meanings.

Why are my USB ports different colors?

UItimately your USB ports can be any color your motherboard manufacturer desires--or all the same color, for that matter--but USB 3.0 ports are often bright blue to distinguish them from older, slower USB 2.0 ports. USB 3.0 devices are backward-compatible with USB 2.0, and the ports look identical, which makes some sort of visual indicator (such as a coat of blue paint or a "USB 3.0" stamp) extremely useful.

Blue USB ports are USB 3.0, black USB ports are USB 2.0, and red USB ports have increased power output.

In a folder full of digital images, I often see a file called Thumbs.db. What is it, and can I safely delete it?

Thumbs.db is a Windows XP system file that contains the thumbnail cache for a particular folder. You can tweak Windows to get it out of your way.

Why does every digital camera--including the one on my smartphone--store photographs in a folder called DCIM?

DCIM (for Digital Camera IMages) is the default directory structure for digital cameras--and having such a standard is very useful.

I've noticed a strange port on my PC. What kind of connection is supposed to go there?

This is a common mystery, and the answer can be any mumber of things. To figure out what your mystery port is and how you should use it, check out our picture-filled primer on PC ports.

My Recycle Bin has disappeared. How do I restore it?

Whether it was the victim of a glitch or was never available in the first place, you can restore your Recycle Bin in a few simple steps.

Where do all of these mysterious Web browser toolbars come from, and how do I get rid of them?

Sometimes spyware installs browser toolbars, and sometimes you do it accidentally during software installation.

How did QuickTime end up on my PC, and do I need to keep it?

This media-playback software comes bundled with iTunes and installs along with it.

I have Microsoft Word installed on my PC. Why can't I open the .docx files my friend sent me?

If you use Word 2003 or an earlier version of the program, you need to pick up the Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats.

Why do some programs leave files and folders behind even after I've uninstalled them?

Many programs' uninstallers are ineffective. It's a good idea to use a utility that removes not only the application but also all of the pieces it leaves behind.

Why do Adobe Reader and Java update so frequently? Do I have to allow it?

Most Adobe and Java patches are made to plug security holes, so you should update them--or use alternative software.

Is it necessary to update Windows?

Yes, you should definitely apply Windows updates for security reasons, but you can take a few steps to reduce Windows' nagging and pushiness about when to make the changes.

You should always download and install Windows updates, but some tricks can make doing so less of a hassle.

Windows asks me if I want to enable Sticky Keys. What are they, and how should I use them?

The Sticky Keys feature makes certain keyboard functions easier to access.

Why can't I send a particular file attachment via email?

The file is probably too large. Check out free services that let you work around file-size restrictions.

How can I determine whether an unknown Website is safe to visit?

Read our advice on how to figure out whether a link is safe from malware or other threats before you click it.

What are the .dat files that I sometimes receive in email messages, and how do I open them?

Microsoft Outlook uses a modified version of Rich Text Format (RTF) to preserve fonts and the like, but the format often causes problems for the recipient. We have three suggestions for coping with this situation.

Don't see your most baffling PC mystery in the list? Leave us a comment and let us know!