I had the same problem with my computer 1 week ago...did u remember before u make the reboot any warning came up?In my case a warning came up from Zone alarm and i denied it twice and after that i couldnt open anything,not even control panel..So i reboot and never got in windows again,i just had a black screen like you,no task manager.Even with safe mode i hade this black screen.
The only thing worked for me was format,thank god i had back up everything 1 month ago so i didnt lose many things.
Hope i helped
Edit : i am using Xp pro Sp2
Edited by Dark19, 18 December 2008 - 03:55 AM.