You still have not tried a restore point. Saying you think you don have any and verifyin it are two different things. We can help if you wont try everything suggested.
As for the Windows installer fix. A quick Bing search turned of lots of results.
How to Repair Windows XP Installer for Free | eHow.com
Windows Installer Troubleshooting
We want to help. But you havent tried everything already asked about.
ok the window xp installer at ehow worked... thanks for the help and sorry for the trouble