Can't boot up in Safe Mode

When i try to boot in Safe Mode in Windows XP, the Safe Mode screen comes up with two users one is one of the two i've defined as an administrators, the other is simply labeled "Administrator". If i click on the former, it brings up the password input box, but nothing appears when i type in the password; if i click on the latter, the machine just sits there with the hour glass cursor, the longest i've let it sit like before powering it down is about 10 minutes. I thought it was a malware problem, but after working in that forum for a while (Thank you chaslang!) it was determined that my problem was a software problem and i was referred to this forum. I have already tried running the Repare Broken Safeboot key in SUPERAntiSpyware, but this did not fix the problem. Any suggestions?