windows freezes on start-up

Hello

I just reformatted my drive and reinstalled windows after getting hit by the Ukash virus. Everything was going fine, doing windows update, etc, when recently, my PC began freezing once it got to the desktop. My mouse moves, but I can't do anything else. The only way to get my computer working temporarily is to restore to previous configuration that worked, but I have to do that on each start up.

I ran chkdsk on boot-up, but there were no obvious errors, and then it just froze again. Can someone plz help?

Mica