First, I booted the system and the BIOS screen would load. Then the Windows XP logo would appear followed by the screen going blank. After powering down the system, I tried booting into Safe Mode. The system would begin to boot and the listing of drivers flew across the screen. Then, BAM! It froze loading Mup.sys.

I started doing research on this Mup.sys problem. I was greeted with a plethora of forums and support sites giving advice on how to fix the Mup.sys problem. Advice ranged from USB hub issues to removing all devices from the system.

To recap: System won’t boot and stops booting at Mup.sys when booting in Safe Mode.

So, I figured lets go ahead and do a repair installation. I’ve always had extremely good luck with repair installations. This is where the fun really began.

I booted off a Win XP SP2 CD and it detected the existing Windows installation and asked if I would like to repair it. I fired off the repair installation and went back to work on other projects. I came back to the system and found an error that I have never encountered before (lsass.exe - An invalid parameter was passed to a service or function). With only the options to select OK or to close the error box, it didn’t leave me much choice. I selected OK and the system automatically rebooted. This turned into an endless loop.

So, we started off with a system that failed to boot and now have a system with a partial repair installation. It’s not looking good.

After going back and doing more research on Mups.sys and trying to force the repair installation to continue. I learned two very important things:

1. Mup.sys has nothing to do with system refusing to boot.
2. Repair installations only repair so much and don’t have much impact on registry issues.

Disabling Mup.sys will just cause the boot to fail at the file before Mup.sys. It just happens to be the last driver to load before the system hangs.

Repair installations don’t fix corrupted registries. It just fixes bad and missing systems files and other related issues.

After endless searching, I came across a suggestion to restore the registry from a System Restore point. Since we don’t have access to Windows, we’ll need to access one of these restore points via the recovery console.

Here is what we need to do:

1. Boot off the Windows CD and access the recovery console.
2. Copy the “System” registry from the restore area to the appropriate place.
3. Restart the Repair Installation.

If you haven’t already attempted a repair installation, you can do steps 1 and 2 and then hopefully your system will now boot successfully.

See this support page: MS KB 307545

The mup.sys error is probably just a corrupted registry and can be fixed by restoring an older version of the registry.