Do you have on-board VGA? If so, remove the GPU and try using that to see if you get a video signal.
Try different RAM slots using only one stick. Alternate sticks if it doesn't work. Make sure they click in all the way on both sides.
I have a processor with integrated graphics and do not have a GPU. I don't really need one for my computing habits. it's a pretty basic setup.
I did the RAM stick shuffle, trying out each card in each slot, one at a time. Sometimes it beeped with one stick in, sometimes it didn't. Then I made sure that the sticks clicked all the way in and the beeping seemed to stop. I put both in, made sure they clicked in firmly, but nothing still appears on the monitor.
Considering the earlier beeping with the RAM, I bought some new RAM. Should be here by the end of the week. If that doesn't work, I guess the problem is either the motherboard, processor, or power supply, but those don't seem like the problem, from what I can decipher with my amateur knowledge.