I noticed this first on my g15 lcd screens performance monitor. My cpu used to show two separate lines in the cpu bar for how much it was using (this was before I formatted my hard drive after having issues with a mobo) and now it only shows 1. I checked in the task manager performance monitor and there was only one box, also realtemp shows only the option to display the temp of core 0.
I thought this was odd, also I didn't get the kind of performance I was used to out of my processor (oh yeah, it's an e8400 btw) so I ran 3dmark to find out what it said my cpu score was. It displayed the following results
SM2.0 score 4641
HDR/SM3.0 score 4695
CPU score 1645
Hey would you open up the device manager and check out how many processor's are being shown there. If there is only one it seems like it would probably be a driver issue. It would mean your computer is only seeing one core. I've also never heard of a processor losing 1 core. Especially if you've never exposed your processor to alot of heat.
Also when you reformatted your HDD did you re-install the same OS as you had on your computer before? This could also associate a software issue. (I.E. Vista to XP)
...By get them from another computer, I meant I used the other computer to go to nvidia's website (mobo is a 750i) download the drivers for gf (8800gts 640mb) and mobo put them on a flash drive, then install them from the flash drive to this pc. Also, I downloaded the most up to date drivers from nvidias website earlier today and installed them.
Well, I did have some problems with my cpu cooler at first, but that was when I built the computer and before formatting the drive...Hmm...I did have to RMA a motherboard (exact same 1 I have now) and just before I RMAd the mobo was when I formatted the drive...(Yes, I really did have a defective mobo, it had a bad PCIe slot ) I did put the same os on the hdd that I had before, but it was a recent (less than a month) XP to Vista (current one is Vista) upgrade.
@Roadrunner, are you sure there should be that many? On Nvidia's site there is only 1 download and that includes all the driver installs. I think it only had 5 or 6 though (didn't actually count so it could be more) for the 750i. I also checked EVGA (mobo makers) web site, and they have the same driver version.
Also device manager doesn't show I'm missing any drivers (I know it doesn't always know what your missing, especially with chipsets).
Dude stop freaking out, there's nothing wrong with your cpu. Sometimes the ACPI or APM doesn't pick up the second core. I don't know if there is a way to pick it up via the software, most people reload the OS. Try and install your mobo drivers via USB or floppy at post if possible.