Upgrade Help

Hi guys, I'm currently running an Intel P5g41t-m LX with an Intel Quad Core Q6600, the latter of which seems to be malfunctioning, Since there are very few 775 processors around where I live, I'm just going to upgrade to a shiny new motherboard and processor.

However, since I'm down at the bottom of the line already, there is a huge amount of choice for upgrades. Could you guys point me in the right direction on what I should be looking at?

The only thing I use this computer for is Gaming and I'd like to keep the cost under $400 but I'll go up to $600 if the gain is worth it.