Then boot into installer DVD or flash stick burned or written using tool and latest ISO for your licensed OS version
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.