|Often when a computer suffers a bang, devices with edge connectors move onto an position where there is oxide.|
Take out all boards with edge connectors (including the RAM and any add-on video card), then clean the edge connectors with a pencil eraser. Pop all devices in and out a few times so that oxide is also cleared of the sockets themselves.
Ensure all connections are firmly pressed home.
I would do this before fixboot, fixmbr, or any tinkering with the software otherwise you might end up adding to the problem.
Please come back and let us know how you got on.