Hi again,
Well we can eliminate cables and GPU being a problem then. Have you tried plugging your monitor into your motherboards graphics port - either VGA, DVI or HDMI. If that doesn't work, then we can narrow it down to it being a CPU, motherboard or RAM problem.
To test whether it's a RAM problem, remove one stick of RAM from your computer, try and boot up. Maybe it will display - in which case you know it's the stick you've removed. If not, do the other one.
If that doesn't work, then you're looking at a motherboard/CPU problem in which case, it's time to look into your warranty I'm afraid
Wish I could help more, but that's now the only thing I can think of if you exhaust the suggestions above.