Sounds like you may have issues beyond this, but:
http://www.pinwiki.com/wiki/index.php?title=A_disciplined_process_to_eliminate_WPC_game_resets
Don't get disheartened; I got two WPC games recently, both of which occasionally reset on me. Sometimes pins just don't travel well....
Check for burned and poorly seated connectors. That's something they seem to skim over at best in the wiki, which was absolutely the problem on one of my two, and at least partially the problem on the other.