I have the issue of the Vista rebooting everytime I get into Welcome login screen. I see a continous disk activity and then after a moment reboots. I can login within that time. However, I cannot do much and can launch task manager at the most. I can see all the process being killed and it automatically logs me off after a moment(around 20 secs) and system reboots.

I loaded this machines registry winlogon hive on a different machine and I see the date value of userinit is not altered and is userinit.exe.

Any other clues