"unable to restart or reset" - really - even when you press the buttons on the case?
If so then you have probably not wired up the case buttons correctly. Also remember that to power off from the front button, you commonly have to hold it in for 5-6 seconds.
Re the graphics - have you disbaled the on-board graphics? .... does it still lock up if you only use the on-board graphics?
In my experience, lock-ups are more often due to RAM and/or software issues such as drivers.