what is the Reasons for reset the FPGA?

[Altera_Forum]

I want to know the reasons that cause the FPGA kit to reset. where I have inverter circuit and it was operating very good but now it work for a moment and then stopped and FPGA is reset. I can't understand what is happening. 

please, any one know the reasons of this problem.

[Altera_Forum]

It could be a power supply failure (even just a few microseconds, if the supply voltage goes under a certain value, the FPGA will reset) or a pulse (ESD?) on one of the configuration pins of the FPGA.