|First, the fact you hear drives and fans spinning and LEDs are flashing does not necessarily mean it's working. It only means those devices are getting power.|
The message is coming from the monitor and not the computer. There's an odd fix here:
(the one by 'pheonix')
It looks like that assumes the computer is OK and the monitor just needs to be reset. Another possibility is the PC is not providing a signal to the monitor and it defaults to that screen. Given your situation I think that's probably the reason. Somewhere in the process of 'putting it all together' you messed up. But try the fix in the link above and see if it works for you .