I've just put together a new computer and one of the cores of my dual core CPU is not working! This is what I have: Motherboard: ASUS P5B Deluxe (P965 chipset) Processor: Intel Core 2 Duo E6420 2.13 GHz OS: Windows Vista Ultimate 32-bit BIOS shows "Count 2" for the number of processors BIOS does not support turning on/off one of the cores My Computer --> Properties shows: Intel(R) Core(TM)2 CPU 6420 @ 2.13GHz 2.13 GHz Device Manager shows 2 processors, both "working properly". So far so good ... Now, the problem: The Task Manager in the Performance tab shows only one Processor/Core--see attachement). I installed Multi Meter(D) (a gadget for Windows Sidebar) that shows the load on each core separately--the second core is always at 0 (even if the first is at 100%)--see 2nd attachement. In the task manager, there are jobs that sometimes run at 90% or so CPU. I've tried to install Intel's INF files "http://downloadcenter.intel.com/Detail_Desc.aspx?agr=N&ProductID=2529&DwnldID=13499&strOSs=156&OSFullName=Windows%20Vista*%20Ultimate,%2032-bit%20version&lang=eng" but that did not make any difference. Both MB and the CPU are still under 30 day replacement warranty from newegg (for another 3-4 days) but I am not even sure which one if any is defective. I'd very much appreciate any ideas on how to fix this or how to figure out which of the MB or CPU is broken.