Motherboard diagnostics?

Not Blender specific, but I thought I’d ask here. I’m having trouble with my computer. I think the motherboard or graphics card is damaged because when I turn on the computer the monitor flickers for 3 hours before it turns on. I’ve tried plugging in an old CRT and that boots up right away but the image is very dim. The computer itself runs fine except for the display, and once the monitor is on, everything seems fine.
The power supply failed over the summer, and I replaced it, but a friend of mine pointed out that sometimes when power supplies fail they can damage other parts of the computer. So I’m trying to diagnose exactly what’s wrong before I try and replace anything.

Does anyone have recommendations for a program that can check the motherboard and CPU and those types of things for problems?
I have Memtest and I’m running that now, but that’s mainly for memory, and I don’t think that’s the issue.

Anyone here with like overclocking experience who uses diagnostic programs? Any suggestions are welcome. Thanks!