For my birthday, I got a gaming computer, it's ok, but reviews about it said that it needs a new graphic card and a power supply because the power supply it has can die pretty quickly and damage the internal parts, I don't know much about computers and I was think about buying this power supply and graphic card but I don't know if they are compatible or if they will fit in the tower, here are the links to the parts.
The computer tower
http://www.amazon.com/exec/obidos/ASIN/B016LO0MLK/reviews-regulararticlelinks-20
The graphic card