Accessing Program Files

I had trouble accessing the internet and was told that my XP was possibly corrupt. Had run CHKDSK,etc. Reinstalled XP over my existing installation and it worked out fine. As far as the internet goes.Under
“DOCUMENTS and SETTINGS” I have two screen names-the original and a variation of the original.Problem is I cannot access none of my program files. A message comes up to reinstall prgrams. I know the problem is in XP signing on to the new screen name. Any help.