I had this problem a number of years ago and switched to an arcade power supply. I couldn't power up a system 11 MPU and thought I had board short for a while. I had just setup the computer power supply so checking with an arcade power supply I found the problem wasn't the board and was the atx power supply. Rather than use a power resistor I just kept the arcade PS on the test bench. Smaller, neater and no fan.

The problem with switching power supplies is that they do not like to be powered without sufficient loading - they will fail without load. The atx ps have no-load protection circuits, but the arcade supplies do not.