New
#21
zas17 you should all ready have a license for Windows 7 and you would need to buy a new license for Windows 10. You cannot upgrade Windows 7 to Window 10 and dual boot to both. You must install Windows 10 to a different partition with a new license. At this point you should be able to dual boot just fine.
It sounds to me that you may have a corrupt BCD store entry which can be fixed but is difficult to explain in this setting. Go into Computer Management and click on Disk Management. Verify that you can see both the Windows 7 and Windows 10 partitions.