Hello, I have a problem with a computer, actually two. A few days ago after trying to turn on the computer, I noticed that the monitor was not going to sleep, and the bios did not emit a characteristic sound when turning on the computer. I didn't take it too much because this situation had already taken place and it was good after a while. Now, however, the situation does not change, I found that the motherboard probably fell and hence this problem. I bought another computer, before checking it with the person from whom I bought it and everything worked beautifully. I came back home with a new computer and how great my surprise was when the situation repeated itself. I found that the monitor probably broke or there is something wrong with the cables. I bought a new cable and nothing else, I borrowed a monitor from a colleague and the same. I have no idea what could be the reason because if in the old computer there could be a failure so new I checked the seller 2 hours earlier and everything worked as it should. What could it be? I am asking for help and thank you in advance.
Looking at the described problems it would not be abnormal ... Maybe something on the network is wrong, or at least only in this one socket / extension cord ??? 
Possible energy disruptions. But the fact is interesting. And certainly abnormal, especially if once there were such "flashes". 