Are you using onboard or installed G/Card
If installed G/Card, remove it an plug display into onboard to test - If it works your G/Card is screwed - If both don't work then its the mother board.
If using on board, theen buy a G/Card and test
This is probably the best way to test if its your card or motherboard.
But also theres a setting in the bios that you may have to change to go from onboard G/card to installed G/card or the other way around. So you might need to check that its set up correctly.
Another thing it may be is the resolution that the pc is set at. If it is that then you should at least see something as you turn your PC on. Resolution only changes when you OS is running. So if u only get no signal when ur OS is running the way to cure this is to run in safe mode and change.
Maybe it could be you graphics drivers? But like the resolution setting you should at least b able to see the start up so u can go in safe mode do reinstall drivers.
My best advice is just plug it into the onboard graphics port which is a default port and work from there. If that fails try a new cable and if possible a different monitor in that port. Try all of these steps before coming to any conclusion that your motherboard is ****ed. Always try the minor things 1st as u dont want to rush in spendin money on new parts that u may not need.
Hope this helps