installed windows 7 twice on different partitions

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Since you have a clean setup, I'd just start clean as above, you would need to mess around with the boot menu likely if you just format the drive, and there may be system files on the other drive from both setups that would cause the system to not boot anymore. Boot off the Windows 7 disk after backing up your files, delete partitions on all the drives, install Windows on C, once that is done, go to disk manager and format the D drive for use.
format D:
Although i would suggest you to backup all your data and start over... remember the space you allocated for D drive and install fresh windows there as its your primary partition and your C is just a logical partition
I would even suggest you to relocate all your disk space (delete both partitions and recreate them with volume you desire)
This can be all done when you insert windows CD and you are prompted to choose install location
 
Since you have a clean setup, I'd just start clean as above, you would need to mess around with the boot menu likely if you just format the drive, and there may be system files on the other drive from both setups that would cause the system to not boot anymore. Boot off the Windows 7 disk after backing up your files, delete partitions on all the drives, install Windows on C, once that is done, go to disk manager and format the D drive for use.
 
Solution