...excuse the long title.
There is a summary at the bottom if you just want the short of the solution instead of the big why and how and for what reason.Story Mode:
I recently had a IBM ThinkPad R51 notebook/laptop computer running Windows XP that would not work in normal mode. Well, it would do the windows loading screen, but then instead of offering users to click into individual desktops, it would present a black screen with a working mouse pointer, but would not allow ctrl+alt+del for task manager or anything else. Keyboard was actually non responsive.
I was, however, able to boot into safe mode without issue. I did the typical stuff: malware scan, startup maintenance, chkdsk...all to no avail, except that I somehow managed to break safe mode. That's right, after my fix attempts, I now have a computer that boots to a unhelpful black screen in normal mode, and hangs at MUP.sys when I boot into safe mode. Boo.
I read tons of forums and wasn't especially inspired by the strange registry hive restoration options or file replacements that seemed to be hit or miss. I decided to start trying something b/c i didn't want to reinstall. A few people recommended ensuring ACPI (ACHC?) mode be turned off in BIOS, or something...I thought I'd start there since it was easy.
Able to boot into the system config (using Enter > F1 to get to BIOS), I didn't see any power saving mode options (ACPI). However, I noticed all the IRQ channels were set to 1 (or was it 11?). I changed all to 'Auto', and found another setting to change POST startup mode to 'diagnostic' instead of 'quick,' which it had been on.
Expecting the same thing, I exited, saving changes. I selected normal boot...and chkdsk tried to start (it apparently didn't remember that it had successfully scanned twice prior to this...perhaps because it never fully booted into windows afterwards?)..I 'hit any key' to skip. Next thing I know, I saw four user icons instead of the now-familiar black screen with mouse arrow. To my further astonishment, clicking on one of them took me right into a working desktop.
Problem solved.
I don't know if my troubleshooting steps actually fixed the problem or if they were coincidental, but probably worth a shot if you don't feel like reinstalling and nothing else is working. Good luck!
Summary:
If you can't boot into safe mode b/c mup.sys hang, or normal mode because you get a black screen with working mouse but non-responsive keyboard, try entering bios setup and setting IRQ settings to 'auto' and boot configuration to 'diagnostic'.
