overclocking help and some help :D?

[zenotix]

My current setup is XFX 6870 dualfan and a 4350 for other screen ,i5 2500k, corsair H60(cpu cooler), 2x corsair vengeance 4gb,
cm storm scout, Cooler master GX 650 W(power supply)

at the start my GPU did work verry good had 80 fps on WoW all the time,and high on bf3 etc,but now wow its like 30 and 40 fps, i have updated drivers and that but still.
and still gets verry hot sometimes over 70C and my screen gets black faint out for 10 sec

and how do i overclock my cpu ?