hey both of you, this is a really easy problem to sort out.
i had this problem with my corsa sxi 2001, cutting out, banging the dash board all that happend to me.
the problem is like one of you said, a loose connection!!!
you have to take the clocks out of the dash board, this is really easy, you can see the join around the clocks, just unscrew all the screws, and take it apart piece by piece.
once you have the clocks out you will notice a plug on the back which is just like a scart socket connection, what happens is over time this comes loose and the connections touch on and off, thus resulting in your car behaving rather oddly. this is why banging the dash resolves the problem for a short while.
disconnect the connection, apply some super glue to the edges and push back into the connector (this is a little tricky). once they are together wait about 10 mins for the glue to set, then put the dash board back together.
there is no need for an auto electrician, if you dont feel comfortable doing this live disconnect the battery terminals.
Well Good Luck!!!!!
Jedi Dave
January 2008