Windows 7 becomes unresponsive on startup

Lately Ive been having trouble using windows 7. Every time i start it up normally it will load to the desktop but then suddenly become unresponsive
and then the desktop turns white (like when a window stops responding) then i have to hard reset.
Right now im running on Win XP (i use it as a backup OS, thank god) and it works fine.

Ive tried resetting the bios back to default - nothing
Ive tried testing testing with only one stick of ram on BOTH sticks - nothing
Ive tried uninstalling some of the updates that were installed before this all happened - nothing

does anyone know how i can fix this? (hopefully not reinstalling Win 7 because that will take me all day to backup, reinstall win 7 and all of my programs/games)