Most computer sites have "certified" replacement parts, besides that check the MoBo for dark areas and see if the silver cylinders on it are popped out or brownish, if so your mobo is shot too.

I did the research for you any of these PSUs should work for your system, yours had a 300W in it so if your adding a GPU id get atleast a 500w

http://www.newegg.com/Product/Produc...&name=MicroATX