I only have guest account on my computer & i can't add another one

[Guest]

Someone got onto my computer & deleted my other user account & now all i have is the guest account & it wont let me make another account for some reason i don't know what the problem is please help!!

 

[WR2]

You need to log on to your PC using the Administrator account.
This youtube video shows you how: How-to Log On Windows Vista as Administrator