Highly doubt the components have died in such a short amount of time.
Have you read this yet.
http://www.pinwiki.com/wiki/index.php?title=Williams_WPC#Game_resetsDoes it reset during gameplay or in attract mode or both?
Is the correct regulator installed in the machine?
You could try to test the 5 volt test point on the driver board and then check for the 5 volts on the CPU to see if there is any voltage drop. Make sure to use a ground on the particular board you are testing to test which will ensure the board has a good ground.
A bit of testing could save some unnecessary work.
