what i suggested to you was the basic method to see if you have a loose connector cable or not....if that is not the case....so the problem lies somewhere else...
do what racer has suggested and follow the steps.
and lastly...go and tell your mechanic that when he cleans your engine bay and uses water....he needs to cover the battery, the alternator, plug the air intake pipe, perhaps the Dcap+wires too just to be safe.
somebody posted a DIY on how to properly clean the engine bay...check the DIY section.