Admin Block

[NoEyesGuys]

I recently bought a computer from someone in my neighborhood, as they were moving and wanted to get rid of a few things. I brought it home and set it up a week later, to lazy to do it right a way xD I started it up and it was fine, but when I went to download minecraft I was prompted for and admin pass. The person I bought it from has already moved and I tried to contact her but couldn't >< any help would be aoppreciated, if the only option is system restore, let me know.
Thank.

 

[Celegorm]

Closing this one as it's a duplicate. Responses have already been posted here: http://www.computerforums.org/forums/software-operating-systems/admin-block-217689.html