You can't stop Windows from going bad.
It's just Bad to the Bone!
The best way to run Windows is from within a Virtual Machine being run under a responsible OS like Linux or Mac OSX.
This way, you can save snapshots of your Windows installation and easily restore it to a point where it was no Badder than usual, or maybe even Less Bad than Usual if you're lucky.
Never mind me, I'm an AntiMicrosoftian