System won't do anything without the CPU fan hooked up, so if you are saying you have not done that, you need to do that. If there is no fan RPM signal, most, if not all systems, won't power up or boot.
It's also possible you have the RAM populated in the wrong slots. Check the manual for the motherboard to verify that you have the same memory slots populated as outlined in the motherboard manual for the number of sticks you are using and that YOU HAVE THE MEMORY FULLY SEATED. It sounds to me like the RAM is not fully seated. Make sure that the locks are fully engaged and lined up with the notches in the sides of the memory modules, and that you installed the memory with the cutout in the bottom where the gold teeth are matched up with the key in the slot as well.
Take a magnifying glass or high powered reading glasses and make sure there are no damaged contacts on the CPU or motherboard. A damaged socket, contact or pin could easily cause this issue.
Make sure you have connected BOTH the 24 pin ATX and 8 pin EPS motherboard power connectors.
What RAM are you trying to run? Model numbers? CPU?
Is the red light flashing or staying solid?