Alyssa, are you under the impression you can only use a Windows 7 Product Key 3 times? This is incorrect.
You can use a retail Windows 7 Product Key, except for OEM version, as often as you want to reinstall wherever you want. Only an OEM version must remain on the same mobo first installed upon but can also be reinstalled as often as you want.
If you bought Family 3-pack then you should have the key with the packaging or it can be audited off another installation using Belarc Advisor.
If not then look in Windows 8 C folder to see if there is a windows.old folder. If so you can roll it back to Windows 7 this way: How to restore a Windows 7-based computer to a previous Windows installation by using the Windows.old folder
Then audit the key with Belarc.