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#21
Is there a BIOS update? If not reset the BIOS to defaults. Set SATA controller to AHCI, save changes and exit.
Where did you get your installation media? I'd eliminate that as possibility by using the latest official installer in Step 1 of Clean Reinstall - Factory OEM Windows 7, wiping the HD as suggested first. Check performance this time before starting updates.
If you tried another HD that would eliminate HD.
That would leave the mobo, installer or bad program or update.