Of all the hassles that can plague a PC user (and, trust me, there are many), few are as infuriating as random lockups.
There you are, typing along, when suddenly everything just freezes. No error message, no bluescreen, just a locked-up, unresponsive system. I've been there. I feel your pain.
If you're a Windows 7 (or Windows Server 2008 R2) user, you may be in luck: Microsoft recently issued a hotfix for systems that stop responding randomly.
What causes the problem? Microsoft says it's "a deadlock condition between the Lsass.exe process, the Redirected Drive Buffering Subsystem (Rdbss.sys) driver, and the Winsock kernel." Well, duh! That was going to be my first guess.
The hotfix is available for both 32- and 64-bit versions of Windows 7. (Fun fact: you'll often see these versions represented as "x86" and "x64," respectively.) To get it, click View and request hotfix downloads, accept Microsoft's terms, choose the hotfix compatible with your system, and then provide your e-mail address.
Click Request hotfix, then check your inbox for an e-mail containing a link to the download. (I'm not sure why Microsoft makes you jump through these hoops, but, then again, I'm not sure why Microsoft does half the things it does.)
If you've encountered this random-lockup problem, let me know if this hotfix fixes it!