Fruit Machine Chat

hi ive got my first mpu4 barcrest machine and im having problems,m red led light on board is lit but thats it,nothing else, was told it was psu so brought one from ebay but still the same, i earthed trhe psu casing with my tester and probed each pin but nothing, i can hear the psu humming, am i missing something obvious, please help. :

Might be the MPU at fault not the PSU?
Red light generally means the Halt light. ANd it doesn't get much worse than that.

hi thanks for that , but i cant understand why if i earth the psu casing and test each pin im not getting any readings, ive checked each fuse, cheers rob