I learned quickly (and you will learn) that this is one of the most common issues WPC games face. Follow the pinwiki link many have presented. Most importantly, approach it from 'least invasive' to 'more invasive' as you troubleshoot.
When I was new, I started this exact same thread. Many people were recommending changing caps, soldering, or sending out the power driver board for repair. It turned out I just needed to reseat the ribbon cable to the CPU.
Good luck.