Yes there are always other things to be fair. Computers are complicated beasts!
If you want to be sure we must start at the beginning.
The next thing is to remove the motherboard form the case and test it on the workbench.
Make sure that you observe anti-static precautions.
Lay some cardboard or use the motherboard box that is non-conductive on the worktop and remove the motherboard/CPU/heatsink/fan/buzzer/one stick of memory and PSU from the case and put it on the cardboard.
Add the keyboard and now I know you haven't got any graphics but try and boot.
The system should try and then fail emitting a series of beeps.
Please post what sounds it makes.