Why might the monitor not turn on intermittently?

Question

Iron

The riddle is interesting ...
I have a fully analog LG LCD monitor and a fully digital ASUS RX550 2GB video card (there is no analog output, only DVI-D, HDMI and DisplayPort), respectively, I connect the monitor through a converter (inserted into HDMI on the video card and has an output D-Sub for my analog monitor).
As a rule, everything works fine, but sometimes, mostly when I unplug (cold) the power cable from any hard drive or CD-ROM, the monitor stops turning on after starting the PC. At the same time, judging by the behavior of the OS, it boots successfully, while the monitor continues to blink the power indicator, which means that it is in standby mode.
It is possible to restore performance in 100% of cases like this: I take an old PCIe video card, replace my own with it, start the PC at least until the first image, turn it off, insert my own and everything works.
Another method worked before, but the last time it didn’t work: I turn off the power completely, take out the BIOS battery, close the contacts to which the battery was connected, hold it for 10 seconds, insert the battery, turn it on - everything works, although the BIOS settings are reset.
The first reaction was to blame the HDMI to VGA converter but it's ok! When, at moments of inoperability, I connected an LCD TV with a D-Sub connector to it, the image on the TV was normally displayed.
Now the version is like this - some BIOS setting changes due to a disk disconnection, and it prevents the monitor from turning on, after inserting a new video card or resetting it, it apparently returns to the "default" state and everything works again. But what is this setting? And how to make it not change? In general, if you have something according to my version, or your own, share it.
PS: the video card has another glitch specifically in my motherboard: instead of a full-screen branded picture from the motherboard (at the beginning of the launch), it shows vertical blue stripes and some colored squares in the lower right corner with symbols similar to the Japanese alphabet. In order not to see this darkness, I disabled the display of this picture in the BIOS, leaving the usual screen with device data.
Motherboard GIGABYTE P41T-D3

Answer 1

Everything. You can finish brainstorming, everything turned out to be prohibitively banal. There was a break in the cable from the video card to the HDMI -> D-Dub converter, but due to the fact that the break was weak, the wire broke only occasionally, just at those moments when I turned the system unit to turn the drives on and off. Once again I am convinced that it is necessary to start solving problems with the most obvious reasons.

Answer 2

Does the monitor not turn on or does not display an image? These are completely different problems.

Answer 3

Maybe the power supply of the monitor, disassemble and check for swollen capacitors.