Help! Just "built" first computer. Sort of. All fans turn. Lights On. Why no signal to monitor?

To POST, you need a good power supply, a good motherboard and good CPU. Nothing else. If anything else is missing/bad, you'll still POST, but get an error of some kind, even if that is just BIOS beeps.

As it's a new build, it's most likely that all components are OK, although it's not unheard of for a component to be bad straight from the factory.

I'd double-check all your power connectors. In particular, did you make TWO power connections on the motherboard? If you only have the one large connector hooked up on the motherboard, the system will behave exactly as you describe it behaving.

If you're sure of all your connections, strip the system down to CPU, motherboard and power supply (nothing else) then test again.

Does your motherboard also have a video card chipset built in? If so, you should hook the monitor to that video port and boot into the system BIOS and set the primary video device to the PCIe slot.

If your motherboard does not have its own built-in video chipset, then something could be preventing the system from starting. Do you hear a beep a second or three after turning the power on? Most motherboards have beep codes to let users know if there is a problem when the video can't be displayed. One short beep usually means everything is ok. Several beeps indicate a problem, and you look in your motherboard's manual for the codes to decipher what the beeps mean. No beep at all means there could be a very basic problem like the CPU not being seated, or a loose / partially seated video card or RAM chip.

Some motherboards have a separate speaker that you have to connect to the pins on the board in order to hear the beeps. Refer to your motherboard manual to find out if your mobo has a built in speaker or if it requires connection to an external speaker mounted in your case.