What 300W PSU do you have? Even though they are both low power cards running two of them on a single 300W unit would be pretty close to the limit for most units.
If you cant figure out what 300W PSU you have post the current limits for each of its 12V rails.
Thanks for getting back to me!
I have the stock power supply that came with my Gateway GT 5220 - AMD Athlon® 64 X2 3800+, dual core processor with AMD64 technology, The only thing i have done to this unit is upgrade the RAM and os to windows 7.
Here is a link of the spec page from gateway if it helps: http://support.gateway.com/s/PC/R/1009151/1009151sp3.shtml#