Wedge,
I am sure this is a RAM issue. Did you try with just the stick of A-Data? I am not convinced that the TwinMOS is a good stick of RAM. If you are going to swp out the RAM, have them give you a matched pair of Crucial RAM that is on the nForce Approved List:
nForceTM Memory Compatibility
As for the power supply, not all Power Supplies are created equal. You will need to look inside the case to find the sticker on the power supply for the information I am looking for. (Since you have an older GeForce card, power is not as critical as someone running a new GeForceFX card pulling 75W for the Vid Card alone.)
Take Care,
Richard