welcome to techimo...you need to post as much technical info about your computer as possible ie make and manufacture of all the equipment motherboard video cards ram drives ect. The operating system and so on .
Are there any beeps?? do the fans spin?? you'll need to be a specific as possible its hard to diagnose problems with just what you have posted
New build? This is one of the most common problems on a new build. Clear the CMOS, reseat the memory, make sure your board is not shorting to the case, reseat the CPU, reseat the video card, etc.
I'd strip the unit down to just what it needs to POST and test that way. This means video, memory, CPU, HSF, and monitor. Test it this way and see if it will at least POST.
Again, check the power supply and see if the board is shorting out against the case. Go over all your wires and make SURE everything is in the right place as it is easy to put one in the wrong place.