The OS install on the hard drive is set up for the old machine, it wouldn't run well (or maybe not at all) in your system. You should format and reinstall.
Getting to BIOS doesn't require a hard drive, you just press DEL or whatever during POST.
Thanks, on my first startup will it try boot into the OS or do i have to push a button to get it into the bios to format the drive and install the new os? thanks