If you have not bought windows license separately from your PC, then it's most likely OEM license.
You may try calling microsoft and tell that your pc mainboard broke, you replaced it and need help to activate windows.
But they may refuse because it's OEM license.
If you upgrade to windows 10, you don't need to call anyone.
And windows 10 supports directx 12, windows 7 - doesn't. That will be necessary for future games.