Mac completely unresponsive to commands at startup

I'm having major hardware issues (ie. graphic distortion, residual artifiacts, freezing up and unable to force quit, computer restarting on its own) so I did some reading and decided to run Apple Hardware Test. However, I've had no success in getting it to run off the original Tiger Applications DVD (10.4.4) or the newer Snow Leopard disc (10.6).

I tried everything possible when restarting the computer; neither "D" nor the "option" + "D" combination brings up the Apple Hardware Test.

The Mac is also refusing to recognize other commands at startup such as:

• option
• C
• command + R
• command + option + P + R

I learned a firmware password could be causing the problem so I triedDisabling Firmware password but it didn't work because it required me to press a key (option) after restarting. I was able to circumvent the issue by restarting from the Install Mac OS X directly after mounting it, and then running Firmware Utility. There is no firmware password in place.

Where do I go from here?