This virus is a biatch!!

Hello,
I am having serious problems with my pc. There was a vius on my pc, think it's called KALBA or something. When I start up my pc, it automatically displays log on, and then I just press OK (I never even activated this before so that it should prompt me with logon details, and must therefore be due to the virus). As I enter windows, it's shows windows has closed this program, something about dll, all a mess. So, then I must do ctrl-alt-del, for my taskbar to open, then go to new tasks and enter explorer for my icons and things to appear. However, I did a AVG scan, and afterwards it said to restart for it to work, which I did. But, now it still shows the logon thing, but worst when I enter windows, it logs on and logs off by itself, I try logging on again, but still the same. I the thought, f*uck this shit, I'm formatting my hard drive and re installing xp. But, now it doesn't even want to read from my disc and do this. It goes directly to safe mode/last good configuration/start windows normally page. I tried safe mode, it still logs on and logs off automatically. What is happening, what can I do??????? Pleeeaaaase help!! Im writing my thesis, need this f*cking pc to work!!