|It's probably not a problem with mup.sys. That's just the last file that normally scrolls down the screen when booting to one of the safe mode options. So whatever the problem is, it's happening after mup.sys loads.|
The bleepingcomputer link recommends fixing via a system restore which probably would work as long as it's not a hardware problem.
You're probably getting a blue screen flash just before it reboots. If you select 'Disable automatic restart on system failure' from the F8 boot menu it should hold on that screen and maybe give you some info on the problem. Also have you tried 'last know good configuration' from that menu?