installed win 8 last Jan. 2014 -online download. So have no disc.
What was the original OS? Do you have a disk for it? E.g. if it is W7 you may be able to use its Command only mode to try using its bcdedit on your W8 BCD; e.g. modify it to boot the way I mentioned earlier.
USed another PC - DELL XPS 750 -another multimedia pc, removed the HDD from the 1st PC, installed here. Same problem --- so now i know it is the win8 OS and not the Kybd and mouse.
So, you could also create bootable recovery media with it, then do the same modification as above.