Sometimes if I turn on my pc than I don't have signal with my monitor. My monitor is connected with my grafic card output via hdmi. If I hold on the on button and restart my pc than I have my signal back. And it happens very often. And also before restarting my pc if I switch my Hdmi cable from my crafic card output to my motherboard output than I also have a signal but if I switch it back to grafic card output than I don't have a signal. So I have to restart my pc to have it back.
Can somebody tell me what the problem is?
It appears that you either have a failing graphics card or a poor connection to the motherboard. I suggest you try removing the card and reinserting it in the same or a different slot in the motherboard.