Lost Password

Can not start OS 10.6.8 because of lost password. Do not have original instal discs so am using Snow Leopard instal disc. When I start up I hold down the C key at the sound of the chime and release it when the Apple logo comes up. Within a few seconds the computer gives 3 loud beeps repeatedly until I power off. I found that 3 beeps supposedly indicates "bad banks". If that is memory I don't understand since I can run OS 10.10.2 using an external HD with no problems at all. Any assist for this portly senior will be happily greeted with smiles.