Disabled Core on Core 2 Duo: Solved?

I joined this site specifically to post this scenario as it speaks about a near "maddening" problem. This will be my 1st thread (ever.. as I usually read), but I felt it was my duty to the tech community, after what I've been through.
It took me 5 days to fix this, and Im still left with the taste of random luck in my mouth.

PROBLEM: 1 of the cores on my E7300 was suddenly disabled & I couldnt get it back.

MY Setup: I had the cpu barely overclocked to 3.0Ghz (5hrs of Prime95 told me it was a stable OC).
I also had a dual boot setup of Windows XP Pro (with AHCI activated) and Windows 7 64bit beta (hmm.. buggy?)
Also desktop was on APC UPS battery.

WHEN: I literally saw my core disappear from the temperature graph. I was glancing at (it was not hot at the time). This occured after I changed something in Power Settings in windows 7, and immediately after signing into Steam. (OS was a fresh install).
I read many forums and tried everything except flash bios cus I didnt think it was a hardware issue. I installed Vista, clicked Detect Hal, went into msconfig / bcdedit.exe, Deleted / uninstalled my processor... Nothing worked.

SOLUTION MAYBE???: What eventually seemed to mysteriously work, is
- deleting the Windows XP partition all together as well as any other OS installs and partitions to get rid of the MBR as I think thats where the problem lied
- Reinstalling Windows ( i just put back Win7, but after this step, still only one core showed in Task manager)
- Go into Device Manager in windows 7 control panel, uninstall these items
Standard AHCI controller (in IDE ATA controllers),
Processors
Microsoft ACPI-Compliant System in "System Devices" (this might remove your usb mouse / keyboard so make sure ur power button is set to restart as you wont be able to use them now)
- Reboot and immediately go into BIOS and set everything to default (Dont start Windows)

- Reboot and turn back on AHCI if needed, check to see if ur board can also turn on ACPI
- Go into windows. (This was the Viola! moment for me)

I dont know if it'll work for anyone else but I swear this is what I did. Resetting my Bios was totally random step! Im still dumbfounded. But i fix my own PC all the time and this is Most challenging issue I've ever faced. I took a nap after.
Cheers.

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