Take out the graphics card, see if the computer beeps. If it beeps either you just gotta reseat the graphics card or it's defective.
Then try the RAM...same thing applies, if the computer beeps when the RAM is taken out, then the RAM is either defective, or just needs to be seated again.
When it comes to CPU's though the only way to troubleshoot it would be to swap it out with another, same applies to the motherboard....so if it comes down to being a CPU or mobo then it'd just be trial and error with RMA's
Make sure you JUST have keyboard, RAM, and graphics card plugged in (and system speaker so you can hear beeps) when you go to troubleshoot.