I'm guessing that the two coin/credit cables go to the same place on the circuit board, which are probably two "push to make switches".
Can you open it up and have a look to see if there is a problem with the connection ?
As gareth says it's worth looking at the coin op mechanism, possibly just needs a blast of ait or a bit of lube. Also do the covers have interlock switches that may have failed or stuck.Failing that try googling "arcade game repairs uk"