I found this online:
to enable hyperthreading WITHOUT reinstalling windows 7:
1 enable hyperthreading in B.I.O.S.
2 load up windows and CREATE A RESTORE POINT!
3 open task manager and click the PERFORMANCE tab, just to make sure it ISN'T working, if it is.... GREAT, but i doubt if it was that easy, that you would be reading this lol
4 click start, then RIGHT-CLICK the COMPUTER then click on MANAGE
5 click DEVICE MANAGER, then double click PROCESSOR
6 right click ANY of the listed processors
7 click UNINSTALL
8 it will say "warning you are about to uninstall this device from your system" click ok
9 click reboot now
10 repeat step 3... you should see all threads