Back up your files, unplug all other HD's and peripherals,
Boot into BIOS setup to enable Legacy BIOS. Next check BIOS Boot order for an EFI Boot Disk: remove it, set DVD drive first to boot, HD second. Then set SATA controller to AHCI. Save changes and Exit.
Then boot into installer DVD or flash stick burned or written using tool and latest ISO for your licensed
here.
At first installer screen Press Shift + F10 to open a Command Box, type:
DISKPART
LIST DISK
SEL DIS 0 (after confirming Windows 7 target HD #)
CLEAN
CONVERT MBR
CREATE PARTITION PRIMARY SIZE=102400 (for 100gb partition, adjust as desired)
FORMAT FS=NTFS LABEL="WINDOWS 7"
ACTIVE
EXIT
EXIT
Next click Install Now to
Clean Install Windows 7 to the partition you created. If it fails then report back at which step and the verbatim error message.
In addition read over these steps to understand the tools and methods which work best to get and maintain a perfect
Clean Reinstall - Factory OEM Windows 7. The steps are the same for retail.