Lost profiles on XP log in screen

This, hopefully, is a simple fix as I’m not very Techy…

I have a Dell Dimension 4400 PC and two days ago all four of the profiles I had on the sign in screen… Disappeared! I powered up as usual and nothing.

I went into safe mode (through F8) and tried everything there but no joy. It just goes back to the log in screen but has no profiles to log on with. I do not have the XP or Dell system restore disc’s as this PC was given to me by an old friend.

Any suggestions as to how I get it back to normal?