To start trouble shooting your issue I would recommend disconnecting all of your peripherals. Only leave your video card connected at first. Take out all of your RAM also. you should get some error message or 3 beeps indicating a RAM issue. If you hear the three beeps (depending on your Motherboard this could be different) then insert a stick of RAM. start the computer and see if it boots. If it does boot, then add another stick of RAM if you removed it, reboot and see if it boots. If it does not boot, then you have a bad memory module. If the system does not boot with the first stick of RAM replace it with the other stick of RAM.
If all works, then connect your peripherals one at a time until your system no longer boots. If all boots fine after you connect all of your peripherals, then it could be something was not seated properly.
Good luck!
Antil0ck