I was thinking that you may have a problem using a USB mouse or keyboard on a fresh OS install but the 780 was manufactured in 2010-2011 so you should not have a problem with this issue. I have very much confidence in Allan's guidance with all the help he's given to me, but I'm just thinking if you have an issue, and have a PS2 mouse - keyboard around, maybe you could try that before investing more. (the 780 has both PS2 ports available)
(Certainly no distrust in Allans judgement here at all, this is just a memory of mine about your same issue that I had with an older PC a few years ago).
Have fun, and good luck!
Mike