Apparently this is a rare
issue. However, it did cost me four days of mucking with my laptop to fix.

The Red Gate ANTS uninstaller doesn’t always remove it’s services, even though the
files are gone. For some reason, this causes Vista to reboot almost immediately after
getting to the login screen. The fix is simple:

SC
DELETE "ANTS
Performance Profiler 4 Service" SC
DELETE "ANTS
Memory Profiler 4 Service" 

>

A couple of commands from the command prompt will clear the services. Try using ‘last
known configuration’ to get you to that command prompt. Safe Mode didn’t work for
me.