To check if the power supply is functioning, look through the vent on the back of the console and look for an LED. If any light can be seen, the power supply is functioning. The LED that is seen through the back vent is the 12v line from the power supply. If no LED can be seen, either the fuse is bad (most common reason), there is a short circuit on the 12v line of the control card (uncommon), or the power supply is bad (rare).
To double check the PSU, use a meter to check that you have 12vDC.