Re: Help needed.....Urgent.
What OS are you using? Xp/Vista? Maybe there is a restore point that you could roll back to? If not you could try running a repair on it with the system disk assuming that you do have that. I should point out that there is some data loss risk involved with this method.
I just read your update about the OS. I was mulling it over and thought maybe it would be easiest to start from scratch? When in explorer do you see your dads user/account? You could always create another user and migrate the data over to the new account, IF its there.