I just built my pc everything turns on but my monitor stays in sleep mode i checked my gpu and its good i checked my psu i che

Neur0nauT

Admirable
Yeah, like 1Liquid has said...check the monitor into the onboard graphics first.

If you are using a dedicated graphics card, then your motherboard is not detecting it. You can set the primary output within the motherboard bios. Make sure your motherboard is set to use the PCIe as primary. This allows the motherboard to check the graphics card slot.
 
Since another GPU isn't posting, it could be the motherboard itself. Have you tried moving the RAM sticks around, trying to boot w/ one stick at a time? You mentioned re-seating the cables, GPU, RAM, ect. Is there more than one display input on your monitor? Might want to try that, or a different type of output on your GPU going to the monitor.