Hi Carlingman,
I find this a useful link when it comes to knowing what power supply you need to run your rig;
http://www.extreme.outervision.com/psucalculator.jsp
Input your CPU, GFX Card, Sound Card, Optical drives, Hard drives and memory and it will give you an idea of what you need to run your setup as a minimum.
I agree with the all knowing Zing

, it sounds like an underated PSU causing the problem.
Give it a whirl, nothing to lose really