How can I fix or repair Windows XP?

I have accidentally damaged Windows XP. I think I have deleted some essential files and XP is not working properly.
Jim, September 2003


done
how do you fix dll errors

robert, July 2008
does this work also for the drivers for printers which were not installed as part of the xp defaults

Mayank, February 2004
System restore!!!!!!!!!!

smith jon, November 2003
Put your Windows XP CD in your CD Drive.
Click on your Start Button and select Run.
Type "sfc /scannow" and click the Okay Button.

Windows will check all the essential files and reinstall them where nessesary.

Kate Line, September 2003