When you say he upgraded to AM4, are we just talking new mobo? New CPU as well? If you have any other compatible known working hardware you can try to swap things around to narrow down where the fault lies (i.e. try swapping out just the PSU, or just the RAM, or just the GPU). In addition to what others said about the standoffs, you could test for those as an issue by removing everything from the case and doing a makeshift test bench on the mobo box if you still have it and see if it boots then. Could even just be a matter of needing to reseat some connection.