I have missing registry keys and corrupted dll files on my Window XP Service Pack 2
Computer. All registry fixers that I have downloaded fail to fix the errors.

(Piggybacked question moved from Introductions to more appropriate topic area.)

If you have a Windows XP CD handy put it in your drive, reboot, boot from the CD, choose to Repair windows. You'll be in the Recovery Console, type SFC /SCANNOW and wait. It should restore missing system files and whatnot. Then reboot and still see if you have the issue.
If you still have it you can try to download Service Pack 2 again and reinstall it, which may replace the missing files or you can boot from the Windows XP CD, choose Install Windows, press F8 to agree, then choose Repair Windows and it should restore all of the system files.