It's hanging on something, probably a non-MS core prog.
Try unplugging anything that is attached to the machine- USB bits, external drives, anything other than mouse and KB......just in case it's a hardware thing.
After that, it would be very useful to be able to get into safe mode- you say 'it won't' boot into it but what happens and how are you trying to access it?
Most machines use f8 on startup (just keep whacking it as the machine
boots up) but some use f2 or other keys.
Can you get to a command prompt ? (start, all progs, accessories IIIRC)
If you can, type the following in
%systemroot%\system32\restore\rstrui.exe
then hit enter and follow the instructions to restore to an earlier point
There are lots of other things to try......there is a small .vbs file you can run that will restore icons and desktop but try the above first and let us know how it goes.