Weird XP Problem

[The Napster]

Ok i was trying to fix my friends computer but i ran into a road block. The system would boot and get to the menu to start in safe mode etc. or normally. After selecting either one (all did the same) the computer would just restart. I managed to fix this by taking out the ram and putting it back in and resetting the bios settings. Now it sucessfully got to XP and logged in. Then i restart it and it asks to do a disk consistancy check which i allow it to do. It starts fixing the disc and gets to somewhere around 96% of repairing the files and the computer restarts again and goes to the disc check again. This time it suceeds 100% but now when it gets to the logon screen it says select username to logon......only there are no users. Just a plain blue blank, as if there are no users on the computer......It didnt use to go to this screen, it would just logon by itself. I tried going into safe-mode to get into the admin account but even that wasnt there. Any ideas as to what went wrong and how to fix it? I had the thing fixed until it disc checked. My last resort is to reformat. Thanks in advance.

[Mak213]

Have you tried a Repair install?