PC doesn't boot but green light on mobo lights up, any ideas?

[Salsa123]

This was a rig I built in August. My stupid friend forgot to switch the voltage switch and the whole thing just shorted out. I RMA'd the PSU and got a new mobo. I rebuilt the rig today and booted but only a green light on the motherboard came on. Any ideas what could be happening?

P.S here are the specs in case they affect anything (I cannot afford to buy new components as this rig is already £200 over budget):
Processor: AMD FX 6300 Hexacore(3.5Ghz)
PSU: Cooler Master Silent Pro M2 620 W
Mobo:Asus M5A78L-MLX3 (AM3+ socket)
Graphics Card: XFX Radeon HD 7950 3GB
RAM: 2x4GB Kingston Blu (1666Mhz)

 

[alexoiu]

Try starting the board outside the case, only CPU and CPU fan installed, both 24 and 8 pin power cables connected.
See if the CPU fan is spinning when starting the board.