I found this some months back, it may help ...
1. Boot into Safe Mode. For instructions on booting Windows XP into Safe Mode, see the document How to start Windows XP in Safe Mode.
2. Log into the administrative account.
3. Click the Start button, then choose Search.
4. Select Choose Files and Folders. The search window opens.
5. Click Tools, then click Folder Options.
6. Click View tab.
7. Ensure "Show hidden files and folders" is checked and "Hide protected operating system files" is not checked.
8. Click OK.
9. Type nisum.dat in the Search box.
10. Ensure the "Look in" box points to your hard drive where Norton Internet Security or Norton Personal Firewall is installed to.
11. Click More Advanced Options.
12. Ensure Search Hidden Files, Folders and Search Subfolders, and Search System Folders are all checked.
13. Click Search.
14. Delete all instances of nisum.dat that appear.
15. Restart the computer. It will boot into normal Windows automatically.
Learn from other peoples mistakes not your own.