Your teacher doesn't seem to know much about electronics...
A Power Supply can't supply too much power unless the component it's attached to is defective and shorting out.
Either way, you're unfortunately down to SWAPPING COMPONENTS anyway to determine the problem.
If it's the motherboard you'd unfortunately have to prove that by swapping out the other components or else have another 1155 motherboard to replace and test with.
Example:
1) Detach all drives (CD, HDD)
2) If there's a graphics card, then swap it or use the iGPU (if you have an iGPU in the CPU).
- to use the iGPU you'd shut down, then attach the monitor to the motherboard (i.e. HDMI, DVI or VGA video)
3) Try a different MONITOR if that hasn't been tried.
Summary:
So I don't really have enough information but again it's basically SWAPPING PARTS. If you get it working then make sure to run MEMTEST www.memtest.org
Also, if it has Windows 7 or 8 then be aware that you can upgrade to Windows 10 which I recommend if you get it working.