A week ago I was having this problem and thought it was my mobo/RAM so I got both replaced but that didn't fix the problem because now everything is built back up again with the new mobo and RAM but I still have the same problem.
My memok! light is on (Asus AM3+ EVO R2.0 mobo) which means bad compatibility between ram and mobo but the website for the mobo says it is compatible with my RAM (G.Skill 2x4GB 1866mhz RAM) so I don't think that could possibly be the problem anymore especially after getting them both replaced so now I'm thinking it is probably my GPU.
I have tried the HDMI and DVI ports on my GPU and no video or audio signal is output so is there anything I can do to fix it or do I need to just get it replaced? Is it likely that it is even the GPU that is the problem?