I hope this will help you even a little. Try to remove your ram for a couple of seconds and put it back just be sure that it is mounted well, or may be the problem is your video card it might also untouched then try also to remove it then cling it well.
But you should try first the ram because a lot of possibilities might be a reason why is that happening.
I have found multiple solutions for the problem that you are having follow the instructions that I would give you.
1. Check your video cards if it is working try cleaning the end of the video card [the pins that is inserted on the motherboard] with a eraser and try to put it back again.
2. Try check your motherboard if it is still working, try removing your ram If there will be a sound but if there is no sound you have a motherboard problem.
3. Check your VGA or hdmi connector if it is not damage, try replacing them.
4. Try putting your monitor to other computers and your CPU (vice versa).
