What is on the other partition? If it's an OS you no longer want, or once contained one, then its best to back it up and delete all partitions during install to overwrite old boot code that can interfere.
If you have further questions post back a screenshot of Disk Management - Post a Screen Capture Image
so we can advise you best.
THe illustrated steps are here for Clean Install Windows 7
. The tools to delete and/or repartition are in Steps 7 and 8.
Other tips here to assure you get and keep a perfect Clean Reinstall
, same for retail.