Unless you can boot the computer from the Snow Leopard DVD your cannot erase the drive nor prepare a hew one. If you have the
Snow Leopard disc, an 8 GB USB flash drive, and access to a computer that can read the DVD, then you can make a bootable flash drive with which to install Snow Leopard...
Most likely it is a corrupted system. I suggest you do the following:
Install or Reinstall OS X from Scratch
Be sure you have backed up your files because the following procedure will remove everything from the hard drive.
Boot to the Recovery HD:
Restart the computer and after the chime...
You will probably like to upgrade any older version software. But not knowing what versions are installed you will need to determine that, then check to see if updates have been released (for third-party) or use Software Update for system updates.
Third-party software can usually be found at...
If there is you would find it at developer.apple.com. You need to register, but registration is free for limited access.
Actually what's saved in PRAM is the same for all models, but different for PPC vs Intel models.
I think you just did them in your post. They are on the right side of the keyboard next to the P key. Unshifted is the standard [] bracket, shifted is the curly {} bracket.