If you have a spare monitor try it with that and see if it works. If it still doesn't work you'll have to poke around inside the case. I had the same sort of problem when i started up my computer a few days ago. I got a yellow-ish orange-ish light on my tower and it wouldn't start up. All i had to do was take out the ram put the same ram back in and it worked. But this just may be something a lot more complicated or not complicated at all. It may be the processor or something else that is vital.