Can't Keep Windows Open in vista! I (rundll32?)

Hi all, I just installed a fresh copy of windows vista (and SP1) ultra 32-bit
yesterday.

everything has been going just fine until today. I did a full system defrag
(online and off) with PerfectDisk 8.0

When I was done I restated the computer and tried to open the My Computer
window. it shows up for a second then explorer restarts. any folder or
explorer window does this. then I look at the task manger and start closing
process nothing works until I get to rundll32.exe its has like five of them
running at once. I close each one until I hit one that can't be closed.

Now everything works fine. I can open windows and all that, but every time I
restart the computer the same thing happens. (note: system restore did not
help).

I've done malware and virus scans but nothing comes up... any ideas on what
I can do to fix this for good? (without a complete reinstall)

thanks in advance.