I am running Norton and AVG. Does anyone know if this will cause any problems or issues?
It will slow down your computer considerably,
I upgraded my avg free edition 2011 to avg free editiuon 2012, but now my pc slows down whenever I start it.
Yes, this will decrease the performances of your computer and will stop some processes. Also, the programs may block each other letting your computer without protection. It is never a good idea to run two security programs at the same time on a PC. My recommendation is to remove one of them using either Norton Removal Tool or AVG Remover.