Boot into Partition Wizard CD to post back a camera snap of the maximized drive map and listings: Screenshots and Files - Upload and Post in Seven Forums - Windows 7 Forums
Normally you'd rightclick in PW CD on Windows 7 partition to Modify>Set to Active, click OK. If partition won't mark Active you may need to convert from Logical to Primary first: Video help on how to set partition as Primary or Logical.
Keep in mind you can only have 4 Primary or 3 Primary and unlimited Logical partitions.
Then click on the HD # to highlight it, from Disk tab choose Rebuild MBR, Apply all steps, reboot.
If Windows 7 doesn't start boot into System Recovery Options
to run Startup Repair - Run 3 Separate Times
. You may need to download the Windows 7 installer with SP1 if the other two methods to access Options fail: See Step 5 in Troubleshooting Windows 7 Failure to Boot.
If these steps above don't work unplug all other HD's which may be interfering - another reason we should see the screenshot first, and you should have asked first if this is something you don't do regularly.