Windows 7 only showing one core on my i7 processor

[punker001]

Can anyone help me? I have recently bought a Dell XPS 15z laptop from eBay and it has an i7 2640m processor which according to the Intel website is a dual core processor. Well the problem i'm having is when I run task manager and CPU-Z etc, only one core is showing under performance. Has anyone had this problem and do you know what the issue is? I have tried pretty much everything including reset Bios etc. If I had any hair I'd be tearing it out lol. Any help appreciated

 

[bassfisher6522]

Have a look at this...

http://www.sevenforums.com/tutorials/66504-processors-limit-number-used-windows-7-a.html

and

HOWTO: Get Windows 7 to detect your new multi-core processor - Microsoft Answers