Windows signs in and then logs off again after saving settings

I need some help here with weird Windows 2000 behavior. I installed AVG and twhen the installation was done, the antivirus found number of virus in the system. I never thought that my 2000 system would be so much infected. The antivirus moved all the virus to vault and it looks that my system is secure. After when I restarted the system it freezed on login page. I get message that Windows is saving your settings and the login screen appear back again. I cannot enter the system at all. I am bit confused with the same. I need some help here to fix the system.

It looks there is some problem with Windows boot. The virus has infected some internal system files which are moved to vault by the antivirus. I found some links that can put more highlight on your problem. Before following any troubleshooting tips try to boot in safe mode and just ensure that all your settings are proper. If nothing works then the last option that remains if re-installing Windows 2000 server back.

Unable to log on if the boot partition drive letter has changed
Windows Log on and Log off immediately.

It is better if you run a repair setup. It looks there is some serious virus problem with your system. I think it useless to work on that system because after few time you are going to get the same problem again. Instead of AVG get a good antivirus which is licensed and powerful enough to deal with the infection. Do not forget to take data backup before going for re-installation.