I am currently using this PC mainly for playing planetside 2 and when it comes to big fights the fps drops to below 24 fps and I wanted some advice about my current pc whether it is salvageable or I should do a new build altogether.

My Current specs:
AMD Phenom 9950 quad core
Centurion CPQ9104 (had to replace old board when it fried)
4 gb DDR3 1333mhz ram
nvidia gtx 280 1gb
60 gb harddive 7200rpm (where I keep game files)
180 gb hardrive 5400 rpm
psu: is good and enough to run my components, however I did make a mistake when purchasing it because it does not have a connector compatible with my gpu so I use two pci-e rails and short a circuit to get it to run.

I am not a massive expert on what games require to run however I would like to improve the fps but I do not want to throw money blindly at the problem. The two things I am looking to do are change the psu( not really sure if it will make any difference) and swap out the small hard drive for a solid state drive. Also I have questions about the motherboard quality as it was a very quick fix when my computer failed.

I look up my components on the benchmark sites and they seem pretty decent quality comparing them to some of the pcs that are currently being sold advertised as gaming pcs, I feel I should be getting higher fps or am I completely off base? Any sort of advice would be gratefully received. Many thanks.