Make your Recovery disks and save a System image as a secondary backup. Back up your files, unplug all other HD's and peripherals,
Boot into BIOS setup, if this is a new Win8 PC look for a setting to disable Secure Boot. Then enable Legacy BIOS or Compatibility Support Module (CSM). This should remove any EFI Boot Disk from BIOS Boot order. Set DVD drive first to boot, HDD 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 OS version.
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.
The purpose of creating the partition above is to wipe the HD and define an Active partition which resolves most install failures. Afterwards you can adjust the OS partition size in Disk Mgmt, create other partitions as desired.