I built my computer a couple of days ago, and task manager showed that 8 cores were running. But now all of a sudden it stopped working. Dunno why. Its enabled in the bios. It was working both before and after the overclock.
What's stopped working? The whole system? Task Manager just showing 4 cores? You need to give us more information.
Why don't you download and run Prime95 and see how many workers it fires off - if you get 8 then Hyperthreading is enabled as you have 1 worker per thread. If you only get 4 then Hyperthreading is disabled or not recognised and you're getting 1 worker per core.
im having the same problem when i first booted my os and mother board drivers i had 8 in the task manager and now all of a sudden even tho its activated in the bios it only shows 4 cores in the task manager im running vista 64 ultimate with 2.6ghz i7