04/14/2022
When a system appears to hang or get stuck on mup.sys most folks assume that there is a problem with mup.sys and set about trying to replace it - but that is a waste of time since that is not the problem (pay attention Microsoft engaged Support Engineer "experts").
When you see that happen, mup.sys has already loaded and the "problem" is what comes after mup.sys.
Most of the time it happens during some kind of troubleshooting effort and the user has somehow either scheduled a chkdsk with error correction to run on the next reboot or the volume on which XP resides has been marked "dirty" - probably from a power failure, reset button, power button, etc.
When XP boots it always checks the dirty bit on all volumes to see if it needs to run a chkdsk with error correction (chkdsk /r) on the volume - and it will do that if it finds a dirty volume. If there is a chkdsk with error correction scheduled to run on the next reboot, XP will run it on the next reboot.
When you boot in Safe Mode and after you see mup.sys load, that is when XP checks the dirty bit on the volumes and it will start a chkdsk with error correction to try to fix it. If there is a chkdsk with error correction scheduled to run on the next reboot it will also run after mup.sys loads.
The thing to do when you see that is to look at the HDD access LED if there is one or listen to the system to see if you can hear the hard drive "working". If there is HDD activity, then XP is probably running the chkdsk with error correction and the last thing you see on the screen will be mup.sys.
The chkdsk with error correction can take a long time - perhaps several to many hours depending on the speed of your system, the size of your HDD, the amount of data on the HDD and what the chkdsk finds to do so the best thing to do is not interrupt it since it will finish one way or the other sooner or later (probably later).
That is why your system finally came to life - the chkdsk finished but you can still check the dirty bit on your volumes to see if it is set or not. Here's how:
Click Start, Run and in the box enter:
cmd
Click OK to open the command prompt window.
To query the dirty bit on drive C, type:
fsutil dirty query C:
Sample output:
Volume C: is dirty
Volume C: is not dirty
Type 'exit' to close the command prompt window.
If the volume is dirty, the only way to clear it is to run a chkdsk with error correction and if the volume is dirty and you boot again in Safe Mode the last thing you are going to see on the screen is mup.sys until XP finishes trying to clear the dirty bit and you will be "stuck" again until the dirty bit is cleared.
There are some other reasons why a system might get hung after mup.sys loads but the most likely scenario is the system is running a chkdsk with error correction - so wait it out.
If anyone wants to see the "problem" all you have to do is schedule a chkdsk with error correction to run on the next reboot, then when the system reboots go into Safe Mode and the last thing you will see on the screen is mup.sys and then you are stuck until the chkdsk finishes.
Note that when chkdsk runs automatically on a reboot either because XP thinks it needs to (perhaps your NTFS volume has been marked as dirty) or you choose to schedule the chkdsk with error correction on the next reboot, the results are shown in the Event Viewer Application log. You need to look there for the chkdsk log to see what happened and any problems after chkdsk has run.
To see the results of a chkdsk that runs on reboot, you must look in the Event Viewer.
To see the Event Viewer logs, click Start, Settings, Control Panel, Administrative Tools, Event Viewer.
A shortcut to Event Viewer is to click Start, Run and in the box enter:
eventvwr.msc
Click OK to launch the Event Viewer.
Look in the Application log for a recent event sourced by Winlogon, something like:
Event Type: Information
Event Source: Winlogon
Event Category: None
Event ID: 1001
Description:
Checking file system on C:
The type of the file system is NTFS.
One of your disks needs to be checked for consistency. You may cancel the disk check, but it is strongly recommended that you continue.
Windows will now check the disk.
Cleaning up minor inconsistencies on the drive.
CHKDSK is verifying Usn Journal...
Usn Journal verification completed.
39070048 KB total disk space.
28017948 KB in 100571 files.
56540 KB in 10556 indexes.
0 KB in bad sectors.
236440 KB in use by the system.
65536 KB occupied by the log file.
10759120 KB available on disk.
4096 bytes in each allocation unit.
9767512 total allocation units on disk.
2689780 allocation units available on disk.
Windows has finished checking your disk.
Please wait while your computer restarts.
