help needed with my computer cpu overheating

Hi my specs are as follows

amd phenom xII 1090t black edition

asus m4a87td mobo

2 lots of 4gb ddr 1333mhz ram

crossfire hd 5850 graphics cards

now my problem is that, i want to overclock the cpu, since its the black edition there is unlocked multipliers, so just use 17, which makes it, 3.4ghz, the computer is fine, but at 18 for 3.6ghz it shuts down and says cpu overheat , i tried turning the voltage up but still same thing,

i just thought the cpu would be able to at least handle a slight overclock with no problems?? what do u think i should try to oc it a little further,

also the case is antec 900 with the standard fans etc,, i don't have additional cooling like water or anything,

ok so i used speedfan to check the temps,

and it reads 69 degrees celcius when the computer isn't doing anything,

that seems way too high, anyone know what could be wrong?and where to start checking

yes the voltage is back to stock,

i turned cool and quiet off, i left the multiplyer default on 16, and upped the fsb to make the processor 3.7ghz,,,

i will purchase some compressed air to clean the dust out, see how it goes from there,

i am not too knowledgable with cooling options,, whats availbale that i can just install, and is the process easy or difficult?