I subsequently Cubase 6.5, 7.0, 7.5, and now I have Cubase Pro 8 and I have
problems with it with an external MIDI keyboard. For elicenser see only
Cubase Pro 8. Do as I install Cubase 7.0 again or will this version work? 
Yours
Grzegorz
On mine 8 and 6.5.5 tun parallel, they both work, check your eLicenser.
Your Cubase 8 license covers previous versions of Cubase. So your versions of 6.5, 7.0 and 7.5 will all run on your Cubase 8 license.
Thank you very much for the information and I am now calm that previous
versions will work.
Yours!
Grzegorz