I suppose you unplugged everything to get the video board out? Could be that disturbing the connectors has resulted in a bad connection. The error messages can be misleading (I have found) and can lead on a wild goose chase.
Carefully inspect every plug that you pulled, and check that the wires are tight in every lead lug in the plug.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)