Overclocking Gigabyte 965P-DS4 and E6420

I'm having some problems overclocking my CPU. I have 2gb 800mhz ddr2 ram and a fairly good graphics card (HD-4850 1gb) but I think my CPU is the bottleneck here as some games lag and changing details or resolution have no or little effect.

Whenever I try to overclock, system shuts itself in some seconds. CPU normally runs at 37 degrees.

Can someone tell me what to do step by step? I tried overclocking to 2.40 ghz from 2.16ghz by changing the fsb from 166 to 200 but my bios reverted back to 2.16 after it shut itself down. Any advices? I have very little knowledge of overclocking from Amiga times

Cooler Master 500W (it says Extreme Power 500W and "RP-500-PCAP" on the box.

Your biggest bottleneck is your ram. 2GB isn't enough for last years games, let alone new games.

In fact years ago when I played America's Army I upgraded from 2 to 4gb and it was a huge improvement.

When you raise your fsb, you automatically overclock the memory, which could cause the overclock to fail.

Set your cpu/fsb ratio (ex: 1:1, 2:1) so that it stays under or near the speed your ram is rated for (ex: DDR2-800)

2.4 seems a reasonable start.