These kind of "black screen" problems are fairly common, but the causes of them are many.

video cards, bad memory, bad power supply, bad cpu, your mobo and sometimes even the devices you had installed.. your NIC, modem, sound card holding down the bus. I'd strip it to it's basics.. only your mem,cpu and video, along with your PSU and mobo. then add your stuff back in if you start seeing video.

Is this a new build ? if not, what changes have you done recently ? oh.. try reseting your bios with the jumper located near your bios chip.. (which should be right next to your battery or a module called an RTC ..real time clock)

edit : IMPORTANT.. when you reset your bios, do it with the power supply cord unplugged or switch on the back of the PSU turned off..