just put blank harddisk in my ultra10. i see no display to show me the
boot> prompt. i don't know what happened....?? Got a third party graphic card. Display was ok. Monitor seems to be ok. i used different one with same result.
sounds like something is either incompatible, or incorrectly configured hardware OR that you losened when you had the case open.
Try making sure everything is seated correctly. Then try again. Also U5s and U10s have quirk that they sometimes need you to remove the power cable plug it back in and switch on after they have been powered off.
If it were me, I would also be using the serial console to debug here, in case it is just the graphic card. As for 3rd party grapahic card, what is it? Is it even compatible with a U10?