1. Try the "Last Known Good Configuration" from the Safe Mode start Options screen.
2. Run the Recovery Console:
A) To run another "CHKDSK" from the XP CD Recovery Console, this time with "CHKDSK /F" to "Fix" errors. Read how-to: How to use the Windows recovery consolehttp://en.wikipedia.org/wiki/CHKDSKhttp://www.windowsnetworking.com/articles_tutorials/wxprcons.htmlhttp://www.computerhope.com/issues/ch000627.htm
Or: B) to Uninstall the Windows Updates that caused the problem:
How to uninstall a hotfix or Service Pack via the Recovery Console?http://windowsxp.mvps.org/spuninst.htm
3. Another option would be to download a live CD (.iso file) to see the hard drive and check, scan, recover, repair, recover the XP serial key, remove Windows Updates or whatever you need/can do with the included tools.
4. Last option would be to repair install Windows XP