This is some feedback I received recently when trying to fix my previous computer. It's good stuff...
If the problem appears to be software related the quickest/easiest fix is to restart the computer. Don't do it with the reboot keys (Ctrl., Alt Delete) and/or the reboot button on your tower/case. Log out of your computer (if possible) and use the "Turn off" button. Wait until you hear it go completely silent and then turn it back on. If something got changed or "twisted" the software will often correct itself when it's made to start over.
If the problem is hardware related, e.g. the keyboard doesn't work. Make sure it's plugged in properly and hasn't wasn't jiggled out of it's place. I don't know 'bout y'all but my cables tend to run by my feet and I'm always knocking something loose.
If the computer doesn't want to turn on at all, check that you have power running to the computer! Plug something else into the outlet to make sure it's still good. AND, if you have one of those power/surge strips make sure it's turned and still working.
If the computer appears to be running but there's nothing on your monitor, be sure there's power to the monitor and that the monitor is properly plugged into the computer.
Determine if you're computer's making any weird nosies. You can turn the computer on without it's case and you should be able to see/hear where the sound is coming from. Is one of the fans catching?? That's how my last computer crashed. It started making some weird noise and it turned out to be the barrings were going out in the fan on the motherboard. I replaced it but should have replaced both... so it crashed.
If you know what you're looking at while the case if off, you might see if there are any wires loose or have come disconnected. If you're diligent in your maintenance you may have loosened something the last time you cleaned it.
NOTE: Don't fiddle with anything in your computer unless you know what you're doing! It's okay to clean it with the canned air (follow directions) but if you're not careful and touch what you shouldn't you can fry (from static electricity) something on one of the circuit boards and then you'll have
two problems! :p
Speaking of cleaning and maintenance... you should be dusting your computer at least once a month... and I don't mean the exterior. By that I mean you've purchased some "canned air" and are getting all that gunk/dust/hair out of there on a regular bases! Be sure to read the directions on how to use the canned air properly and be sure to read your computer's instructions on how to best clean it too.
If the computer is running slow, when was the last time you "defragged?!" I'm really bad at this and will go a year without running this maintance process. If you go to Start, Programs, Accessories and then System Tools. There's a selection there that's called "Disk Defragmenter." What this does (in very simple terms) is place all your files, programs, whatever in a very nice neat order so that the computer can more easily (quickly) access what you need.
I'm sure there are a few (if not several) other things we can do at home to troubleshoot issues that arise. Please feel free to add any follow up suggestions.
I think it's important to try and figure out minor problems on our own. I was at CompXXX recently and their tech cost was pretty steep. Worse (for me) than than the cost is the possibility of being without my computer for 24 - 48 hours! Yikes!
Good luck!
ED