Try A Repair
Sometimes, even with my fix, your system could still be acting strangely, as it's beyond a few simple changes.
What you can do in this situation is get the original XP CD that came with your computer and attempt a repair with it.
If you cannot find the XP CD that came with your computer or if you do not have one, you can call your computer manufacturer and see if they can ship you a CD.
- Boot the CD
- Press any key at the prompt
- Wait for all of the files to load
- At the new prompt, push Enter
- Accept the agreement
- Your XP CD should find your current Windows installation and offer to repair it