Symptoms: 1. When booting in normal mode my windows XP system hangs after displaying the XP logo and progress bar. A black screen appears and then.. or 2. When booting windows XP in safe mode the last driver that shows loaded is mup.sys. Then... or 3. Instead of XP freezing at mup.sys windows reboots itself repeatedly just after that driver loads. Then there is a flurry of HD activity and all the LED's on the kybd light up and then go out. The Keyboard is locked up and dead at this point. There is some minor HD activity with maybe 3 or 4 blips. Usually the mouse laser cycles at this point but goes out. You have the classic Windows XP frozen at mup.sys. The variation on this is that instead of XP being frozen at mup.sys it actually resets itself after loading that driver in an continuous loop. Both cases can be considered the same issue as we address them here. Many users have run into this problem and there are many different causes and just as well even more solutions. This shows as a hang at mup.sys because after mup.sys loads, Windows then goes into a more complicated portion of its boot process and this is where the actual hang occurs. So, What happens after we see the mup.sys driver load on a safe mode boot? The windows OS is looking in the registry, executing PnP (Plug and pray) and ACPI routines checking the components and resources found. It then starts these components possibly causing more draw on the power supply. Consider here the load of non-self-powered USB devices. If there are any unrecoverable problems here, that will cause the system to hang and it will look the same. - The system hangs during a safe mode boot after loading mup.sys! The main reasons for this Windows XP or Win 2000 boot hang or alleged mup.sys issue are:
In my experience, I have never found that the mup.sys driver is actually the cause of the problem but replacing it with a known good uninfected version won't hurt if just to exclude that possibility. Also, disabling the mup.sys driver by using the recovery console normally does not help either. Windows will then just hang at the driver that loads prior to mup.sys. If you are curious and want to know more about this driver check out the What is MUP.SYS and what does it do? section below.
Here are some troubleshooting suggestions with the more frequent causes and resolutions colored dark blue:
As I stated above it is highly unlikely that mup.sys is causing your boot issue but maybe you're curious. Just what in the world is mup.sys anyway? Glad you asked! MUP stands for Multiple Universal Naming Convention (UNC) Provider. uh huh. That clears it up doesn't it! OK, How about this: mup.sys is a kernel mode network redirector used as part of the Windows Installable File System (IFS). Still as clear as mud? Maybe if I give an example of what mup.sys does it will become more clear. Basically MUP comes into play when an application is trying to perform an operation that involves a remote filesystem resource. Mup.sys acts like a router that calls the correct networking method to provide communication to that particular type of resource. For example, If you wanted to use notepad to read a remote file on machine "fileserver1" the path might look like this in UNC format: \\fileserver1\user\joe\readthis.txt
I have greatly simplified this process, especially in regard to the network provider functions in item 4 but I think you will get the idea. So what does mup.sys have to do with a boot freeze or loop issue? Most likely, nothing. The only possibility that might even be relevant is the instance where your system uses mapped network drives. This paragraph is just for your edification and satisfy your curiousity on what mup.sys does. As stated above, I have never seen a case where mup.sys is the actual cause of the black screen of death on boot issue. It is just the last thing you see on a problematic safe mode boot, nothing more! Here's a challange, If you ever experience a situation where mup.sys itself is the cause I'd be most grateful if you could let us know by sending an Email or submitting a message from our Contact Us page. With your permission, we will post that here for the benefit of all acknowledging you with full credit and\or a link to your article if you wish.
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