Before you start, there are TWO power connectors that must be BOTH plugged into the MB to get it to work. Make sure both connectors are securely plugged in. "No post but fans running" could be you only have one plugged in. Look in your MB manual - they will show you which cables to connect.
Standard debugging is to pull parts until it beeps. (power down before pulling a part, do not install or remove parts with PC powered up). I leave the case open. Eventually you either ...
1. start getting beeps: put the last part you uninstalled back into PC. Do you still get beeps? If yes then keep adding parts back in. 'reseating' the part may have fixed your problem. If beeps stop when you put the part back in then suspect that the last part is bad (or less likely the connector where you plug the part into the MB).
2. Get down to just the MB, CPU and power supply. If you get here you need to pull the MB from the case, put it on some cardboard then hook up just CPU, MB and the power supply. No other wires connected. Short for a moment the pins that go to the power switch to start the PC. Does it post? No, then pick either the MB or PSU to swap. IF you have another PSU that you can use this is where i'd start. It's rarely the CPU.
If this doesn't help, say so then write down all your parts including description and model #. That will make people more apt to help. edit: they can find things like "this cpu doesn't work at this MB bios level" or "only put memory in this slot not that one"