You have a problem, but you're not sure what it is? Start out at Computer Hope's list of software and hardware problems. Even if you can't figure out what the issue is, you'll be able to figure out what it's not before you call tech support.
For Windows users needing a little more in-depth assistance, Annoyances is kept up to date with tips and tricks for navigating Windows, from Windows 95 through to Windows 7. (www.annoyances.org/) In a similar vein, the forums at Techguy are constantly active and incredibly useful if you have a problem that needs a fast solution. (http://forums.techguy.org/)
DLL Downloads & Microsoft Knowledgebase
One thing many of us face from time to time is a missing DLL file. Fortunately, DLL Downloads (www.dll-downloads.com) keeps copies for you, just in case you don't have your Windows or software install disc handy (and if you need to know what the DLL does, Microsoft's knowledgebase can help.
On a similar line, there's also this site dedicated to helping you figure out which extensions belong to which program - if you haven't figured out what will open ‘importantfile.wks', this site's for you.
In these days of YouTube, installing a new piece of hardware is as straightforward as finding the right video step-by-step guide. We're quite fond of eHowTech's channel, which walks you through various installations as well as guides to more esoteric functions, such as overclocking a processor.
PC Hell Beepcodes
If you've got your hardware installed, but things aren't going well, then hardware troubleshooting is readily at hand. If your machine won't even start, for example, you can check the beep code decoder to find out why. Once you can get into Windows, don't forget that Safe Mode can help, if nothing else
Australia's own Whirlpool is an incredible resource, filled with knowledgeable folk from all walks of life. While the site's "official" coverage is confined to ISPs and internet, you can often get an answer to almost any problem there, or at least locate other people with the same issue.
And if all else fails, and you need someone else to step in, why not try Gizmo - its helpful tech support staff will come to your door, install hardware, solve software crises, and even recommend products for a specific home setup, if you so desire.
Despite a certain company we all know and love saying that their products just work, sometimes they don't. If you have a Mac, then Apple's support site is comprehensive as a starting point for assistance; head to Mac 101 and follow your problem to its solution.