The only real way to deal with such an issue is to reinstall Windows 7. If you want to access the data on the drive then remove the drive from the PC and attach it to another PC that you do have access to which will allow you to access and remove any data you may wish to keep. You can then reinstall Win 7 and set up a new admin account which will allow you control over the computer.
If you have problems doing this yourself any competent technician will be able to do it for you. Take it to the shop. Tell them you want a copy of all data on the drive and a reinstall to take place after that.