Looks like you got the penalty for buying a low priced system which use MicroATX power and have the video and sound etc on chips on the Mobo. You may not even have a slot to plug in a decent video card. Certainly don't have enough power to run a good video card.
The only key is the physical size of a new drive, if you have one of the really small MicroATX cases. PC Power & Cooling should guarantee what you buy.
I want a new power supply, so i can play Movies and games in surround sound without it crashing on me; any ideas of power supplys