This was my first thought as well. That mobo will definitely need a bios update for the 3450 to work.
Yes, that was the problem. I had not updated the BIOS before the new processor. Had to remove it, reinstall the i3-2120 and it POSTed normally. Then I updated the bios, reinstalled the i5 and now everything works fine.
Thanks for the help, guys, really appreciate it!