|Are you always using the same data cable to connect the monitor in all instances, including now?|
If so, the problem may have something to do with one leg of the PSU. Probably the 12V. If you have a compatible substitute PSU I would try that. Also, check the 20/24 pin power to motherboard connector.
Inspect the motheraboard for any signs of bulging, leaking, burned, etc. components.