PC World put out articles here
on outer stuff you can DIY rather than buy a new machine. For often the problems are really annoyingly small, not even due to Windows messing up. Then what? Especially, if your lappy or cord gets banged up...
Both articles (latter is a slideshow) cover six repairs: cord, casing, cooling fan, keys, scratched screen, wet. Examples are all for lappies, but you can quickly see how a desktop or tablet might be analogous.
For a somewhat overlapping list, yet covering a wider variety of problems (including iPod and dead pixels), click here.
To me these repairs aren't as easy as they sound, but what if you have no time or money or inclination to futz with a new PC?