Can only get it to boot from disk

After a long, confusing fiasco trying to reinstall the OS on it, replacing cables, swapping out disk drives, amongst other things, I FINALLY got something other than the blinking question mark folder. (which was quite a feat for someone who knows nothing about mac's albeit a fair bit about pc's) Only problem is that I forgot that I had unplugged the HD trying to get it to boot at all. So I plugged the HD back in and all I get now is a blank white screen and no activity from the dvd drive. I tried reformatting one of my pc HD's with macdrive 8 and tried again but I get the same blank white screen. Any help, thoughts or suggestions would be very greatly appreciated, I've been on a mission trying to get my antique up and running and have come so far....I can feel I'm so close!! Please help???