Windows 7 lost administrator account

Have had my Dell laptop for 1 week, came with Windows 7. The dell/windows setup had set me up an account as an administrator (the only account set up on the PC). For some unknown reason this account has changed to an account type of 'guest' and now I can't change it. If I try to do anything with security, like changing the account type or adding a new user I get a message asking for the administrator password to continue, but in that message it doesn't even have a place to key a password! I'm completely stuck for what to do to correct this.

Gave up trying to fix this and did a factory restore.