can't install Service Pack 2

I tried to install Service Pack 2 and after installing, my computer
continually restarts. I get a blue screen every time as well, but I can't
make out what it is saying as it disappears so quickly.

I have tried installing it from Automatic Update and from Microsoft's site
and I get the same result every time.

Can anyone help me? I want to switch to Vista, but it says I need Service
Pack 2 installed first.