what will happen if i activate two copys of windows on the same pc with one product key

[ter p]

I got windows 10 as my main one but I find a pain to top up my pay as u go electric and gas because british gas only use windows 7 so I got windows 7 on a partition I have not activated 7 because its same key as 10 but it will activate it asks me to activate it what do I do. not buying a key .

 

[Suztera]

You can use it on Window 10:
http://www.britishgas.co.uk/content/dam/british-gas/documents/HETU_Windows_10_workaround.pdf

 

[glamdringfh]

Suztera has found the instructions you need to access the british gas suite on Windows 10.

To answer your other question, you shouldn't use your old Windows 7 key on any other active drive now that you have upgraded it to Windows 10. It is a violation of the Windows EULA and will most likely result in Windows flagging your key as invalid.

 

[USAFRet]

1 license key, 1 installation.

If you had Win 7 installed and then Upgraded that to Win 10, you can't continue to use the original Win 7 license key.
One or the other will become deactivated.

Now...if that Win 7 license was NOT Upgraded to Win 10...then sure, you can use it. It is a whole other license. Right?
How many licenses have you purchased? 1, or 2?