1. Your Wi-Fi network is now dog-slow. If it's not a network outage, you likely have interference. Try relocating your router to shield it from disruptions such as microwave use or calls from a cordless phone. Or you may be on a crowded channel. Change the channel via your router's configuration page; look for a 'Channel' section and try 1, 6, or 11. See "How to Improve Your Wi-Fi Network's Performance" for more ideas.
2. Your display looks terrible. Check display settings by right-clicking the desktop; choose Properties in XP or Personalize in Vista, then Settings. If you can't increase resolution and color quality, click Advanced, Adapter. If Standard VGA Adapter or another generic adapter is listed, download a driver specific to your PC (see How to Reinstall Windows XP for details on doing this). If your adapter is there, try a prior driver version. In XP, click Properties, Driver, Roll Back Driver; in Vista, open the Personalization Control Panel, choose Display Settings, Advanced Settings, Properties, and click Driver, Roll Back Driver.
3. Your printer is spewing out garbage. A cancelled print job may not have cleared properly from the printer's memory. Turn the printer off for a minute, then back on. While you're waiting, go to Start, Printers and Faxes in XP, or Start, Printers in Vista, to delete anything in the print queue. If the problem continues, download and reinstall the driver.
4. Your default printer is no longer the default. Some apps, like Microsoft's OneNote, install faux-printer-like devices as output options, and some will also unhelpfully make them the default for all print jobs. Select Start, Run, type control printers, and press <Enter>. Right-click the printer you prefer, and click Set as Default Printer.
5. You see daily, consistent error messages citing memory problems. To check if bad RAM is actually the trouble, download the free MemTest86 and stick it on a boot disk; then run the full battery of tests.
6. Your PC starts up too slowly. Click Start, Run and type msconfig. Then click the Startup tab to see all of the apps that load at startup. Uncheck anything you don't want to start at boot-up--but uncheck programs one at a time, as you need many of these apps to run your PC. (For more on pruning safely, see How to Make Windows Start Up Faster.)
8. You broke a key off your keyboard. If part of the key mechanism is broken, consider scavenging an unused key (<Insert>, perhaps) and use its mechanism with your broken key (Apple's tutorial at PowerBook G4: Keycap Replacement will walk you through the procedure--it should work for almost any keyboard). Replacement keyboards for laptops can usually be found on eBay for $40 or less; many step-by-step guides show how to do the job, such as the one for a Toshiba laptop keyboard at Laptoka.com's page, How to remove and replace laptop keyboard yourself.
9. You bent a pin on one of your PC's ports or cables. Using pliers will probably make things worse, but the tip of a large-diameter mechanical pencil will fit most pins. Just slip it over the bent pin to straighten it out.
10. Folders show only large icons. Change the default in Windows Explorer by setting the right view on any folder, and then click Tools, Folder Options. Click the View tab, then Apply to All Folders (Apply to Folders in Vista).