Run "SFC" the system file checker. Do not replace the USER, GDI, or KERNEL, because usually if you do, it will hose it up more. But see what it says. 95 may not have it, but 98 and up should. If files are damaged, it will attempt to repair them.
Click on the Start button
Click on the "Run" command
Enter SFC on the pop-up Window that Run brings up.
Follow the instructions on the form.
See what it says, and again do not replace your USER, GDI, or KERNEL files if it asks you to. Instead, consider a RRR or Reinstall if these are hosed up.