If you didn't enter your own adminstrator password when you first got the machine, then presumably it will be whatever Packard Bell uses as its default password. Why not contact them and ask them? You may find that it's something simple like "password" or "admin" or "default".
Alternatively, when you originally bought the computer, did it come with a Packard Bell restore CD? Or did you create one yourself? My Packard Bell (about the same age as yours) came with software that allowed me to make a full system restore CD that would restore the computer to its factory settings.
If you have one of these CD's, put it into the drive and then restart the computer to boot from the CD (you may first have to change the boot order in your BIOS). Then follow the instructions that the CD restore program will give you. You'll probably get two choices - a Windows repair (which will preserve your data) or a complete restore (which will destroy all your data and any software that you have installed on the machine).