Can't update from Windows 7 but clean install worked

I had Windows 8^^^^cracked and got a Dreamspark key for Windows 7 from my college. I installed Windows 7 so I could upgrade to 10 in a legit way. The upgrade process didn't work.

When Windows forced the reboot (at 30%) I got a black screen and no mouse cursor. I had to manually restart the PC. Then it recovered and kept going. At 75% rebooted again and another black screen. This time restarting the PC caused Windows to revert the upgrade and go back to Windows 7. I tried this a few times and eventually gave up.

Tried a clean Windows 10 install and well, it worked. So now I have a valid Windows 7 key that I can't upgrade and an unactivated Windows 10.

What can I do? I'm seriously considering just cracking this again.

My PC:

Intel Pentium G860

HD7770

4GB RAM

Thanks