Being a computer tech for a few years, and having to diagnose infront of customers on the spot I have a few quick tips for you to test your stuff. The first thing you would want to do is try with a different PSU, it is unlikely that it has failed, and is still powering the system on, but as everyone here knows; you cannot eliminate anything until you try it (because I have seen one or two cases where that had occured). Just as a quick test without replacing the power supply (which I DO NOT suggest replacing the power supply...), would be:
To test the motherboard; make sure you have the mini-speaker plugged in on your Front-Pin-Headers, or that there is one integrated into the board first (most have an integrated speaker(well intel boards anyways..)).
1) Completely pull out the RAM and videocard both at the same time (obviously while the system is off...). If the system beeps and complains that is has no video or RAM when you turn it on; your issue is not your motherboard or CPU. If it does NOT complain and beep like crazy, then there IS an issue with either your CPU or board.
2) Testing a CPU is impossible without having either another motherboard to plug it in to, OR having another CPU of the same socket to try in your motherboard (although this doesn't help you with the fact that BOTH may possibly be dead...) Depending on the area you live in, if you take the CPU into a local PC shop, they may have a "Test Bed" motherboard that they use when fixing PC's to plug the CPU into to verify functionality.
3) Good luck with that
. No POST issues are very easy to fix if you have lots of spare parts lying around, but at home they are very difficult.
4) I'd say about 90% of the time I run into a NO POST (unless it is a newly-built machine), the problem is the motherboard, just like most of the other people in this forum have stated.
5) Sorry for the long-winded post, that's just me.
Best Regards and God Speed!