I am running Windows 7 Ultimate 64bit. It has been running well, but recently I noticed that one of my cores from my core 2 duo is not being shown in the task manager, msconfig or speedfan.
In the task manager, there is only one graph, and the view>cpu history>one graph per cpu option is greyed out. In msconfig, under the boot configuration options the drop down list for the cpus to be used at boot shows only one cpu. In speed fan, there is only a "core 0" temperature graph.
I have tried clearing the cmos, this made no difference. Also, I have tried two Linux live cds which both happily use both cores. The interesting thing is that in the device manager it shows two cpus just as normal.
Does anyone have any ideas?