AVG Antivirus 8.0’s recent set of antivirus definitions broke Windows XP by quarantining XP’s user32.dll as a bad file.
There are 2 ways to fix this:
Windows XP CD – If you have a Windows XP installation CD handy, follow these steps.
No Windows XP CD – Grisoft has created a bootable .ISO or bootable flashdrive image. Follow these steps to repair your PC. (Need to burn a CD from that .ISO? Use the free utility ImgBurn.)