OK, many people are probably asking the same question. Is the bolded selection above the problem you are having? Saying that your computer has suddenly stopped working is very vague. Please elaborate
If this is the case, it could be various things, for example:
When the computer fell, something on the motherboard could have been pulled lose or thrown out of place (CPU, Capacitors, Resistors)
If this happens there could be a short and signals are not being transferred properly.
The power supply, this could be the problem.
Just because the power supply is plugged in properly, does not means it works fine, power supplies fail all the time. All the fans could be turning on but that one cable running to the MB may not be working.
Hope this helps