You may want to consider getting a new power supply , maybe at least a 500w , I don't know what you will be doing with your computer but 300w is not very much when you look at what you have for components.
You have a very nice spec, but you won't go far with the PSU though. The only graphic card that can run with that PSU is Radeon HD 6670. If you upgrade you PSU to 600W-650W Corsair, Antec or Seasonic, you can upgrade to Radeon HD 6870.
thanks for the help. I just installed a conair gs600 and it would not power up. checked connections but could not get it to work. so I put in my old one and it powered right up. guess it might be a dud.