Why is my i5 2500k running at 1.5ghz?! please help

[idata]

when i was done building the computer, assassins creed revelations was working fine. when i check http://www.tomshardware.com/forum/322422-28-2500k-5ghz# CPU Z and my asrock tuner it says its at 1.5ghz and assassins creed is lagging now. my multiplier is at x16 and i havent touched anything. whats going on?!

SPECS:

ASROCK extreme 3 gen 3 mobo gigabyte 6870 1gb 500gb WD sata 6 gb/s http://www.tomshardware.com/forum/322422-28-2500k-5ghz# core i5 2500k with stock cooler (3.33ghz)

screen shot attached ...... http://i44.tinypic.com/161mfza.png http://i44.tinypic.com/161mfza.png

PLEASE HELP

[idata]

here is a screenshot with prime 95 running and my clock speed didint go up. http://imageshack.us/photo/my-images/841/primer.png/ http://imageshack.us/photo/my-images/841/primer.png/

[RGiff]

You can turn off intel speed step , but that is a normal function at idle . you would have to put a load to watch it throttle up to Reg Spec. , your CPU volts seems low. check that .