On the Safe Mode screen...
Have you tried the Last Known Good configuration?
Have you tried the Repair your computer option?
Have you tried both passwords in both accounts?
'Last known good' doesn't work - get to exactly the same point before restarting.
Tried every possible combination of accounts and passwords in safe mode, with no sucess, and after about 40 secs the computer restarts and the cycle beginsa again.
Also tried every option in the 'F8' menu, with no joy.
The only option which seems to get me anywhere is the 'repair your computer', which lets me log in as admin and open command prompt.
I ran chkdsk, which reported no problems found, and also ran the memory check tool, which also reported everything as being fine.
Sorry if any of this seems vague - I can only access the internet at work at the moment