tips to upgrade an HP desktop

Right now, its Intel Q8300 @ 2.5ghz(stock), 8gb of ram(stock), XFX ATI 4650 1gb DDR2(upgraded,got it as a gift a year ago), 300w psu stock. runs BC2,MW3, BOPS and LF4D2 on almost max settings.

My rig uses LGA 775, so there are not many CPU options available, I was thinking of upgrading the graphics card and psu and keeping it for another year since I'm tight on money ($250-$300 is the most I can spend). Also, I can't overclock since my mobo is locked due to being from HP.

Or end up building a whole new system from scratch saving $$$ of parts I already have like a case, cd drive, etc.

What do you guys think?

I will be ordering the parts from newegg.

If you can get a new mobo for cheap, you should get one that enables overclocking the CPU. Otherwise, just leave it be and get a new graphics card (6850 or better) and a new PSU . You will be CPU bottlenecked in some games (e.g. starcraft) but it shouldn't be too bad). FPS games such as BC2, MW3, etc. shouldn't really be affected, especially with some overclocking. I don't know about HP, but I know Dell uses their own propriety PSUs. If that's the case, you would probably have to get a new case too. Whether that's worth it or not is up to you.red12355