User accounts screen blank

Hi, newly registered but was on before with a different screen name, not that it matters too much. Anyway, I was given a Dell laptop, an Inspiron 5100, in classic shape...all junked up due to zero maintenance. I've run Glary, crap cleaner, superantispyware, wise registry and disc cleaners, defrag...the usual suspects. What I want to do is delete the previous owners two accounts, and now I can't see them. Doesn't matter which account I log into. When I go to user accounts in control panel, the screen is blank. I've tried many times in all accounts and there's nothing. I was able to create my own account initially, but now I can't even see that. I don't suppose that it matters too much at this point but I'd rather have the one account as part of my effort to bring this thing back from the dead. FWIW, it's Windows XP, Pentium 4 2.something ghz, 512mb ram though I don't think the specs have too much to do with this issue.