If you're getting 4v on the 5v rail, you may have blown something on the main board - check the 3 fuses on the main board near the display connector. These are only generally blown if the display board connector is plugged in a pin out.

The low voltage could also indicate a high current draw on the display board due to a short.

35v explains the dim display, but you need to look for the reason why. I can't remember the 60v display cct off the top of my head, but it may use the 5v supply divided down as a reference, which would mean if 5v dips, so does the 60v supply.

Hugo