A few things to check. Ensure that the memory module is properly seated and (as already mentioned) the CPU fan is connected to the correct fan header on the motherboard.
There are two power connections to your MB. One is a 4-pin connector located near the CPU and the other is the 24 pin header. Both need to be connected and properly seated into their respective connector sockets.
If you have a CPU speaker, hook it up to the speaker output pins in the connector header so that you can hear any beep codes that might be generated.
With luck, this is a simple problem with a connector not properly seated.