BFG 8400 GS on a Dimension 4700? Not working...possibly.

Hi everyone. I just upgraded to a BFG Nvidia 8400 GS and it doesn't look like it's being used effectively. I have the standard Dell 305 W Power Source (Card says it needs 300W) and GB of Ram, but when I play Spore the defaults are all set at the lowest levels, plus I Don't really hear too much noise from the card (tho it's onboard fan does run). Also I have the last driver from Nvidia (183 I believe). Does the 8400 GS just not run on the Dimension 4700? While I'm on the topic, I've dismanted the computer and I cleaning out everything since it's loaded with dust. Can I "open up" the source to clean out the insides of all the dust or is that not advisable? Thanks in advance!

Jeff