Most human beings have an almost infinite capacity for taking things for granted.
There's a good number of things to do to your PC on a regular basis to keep its innards healthy and its coat shiny. Scan your disk quickly. Use ScanDisk or Norton's Disk Doctor to check for problems, cross-linked files, etc. If you like, you can put a program shortcut in your Startup folder so you automatically scan every time you start up Windows. At the end of every day, back up the files you've modified.