usually there is a hidden admin account ...try this
boot pc in safe mode ( hold F8)
select safe mode with command promt
when the box comes up type
net user administrator /active:yes
it should say , succesful
reboot
try and login with the main administrator account that has just appeared
create a normal account with admin privledges incase things go pear shape
also try and reset the password on the account if u have one,
if not you will have to copy the files over through c: and then maybe create a new account