Display show no input signal is why ah

I would like to ask you, oh, my computer students in the past has been used very well, but then they put it hard admit another plug a hard drive, then the machine will not be able to start and then come back or not-for-plate line , And always display shows no signal input, and then do not do the normal boot time machine to ring them out, and that Taiwan does not sound machine, is why ah? How to repair?, I re-inserted N times the memory, the display is good The show card is integrated

display show no input signal is not incorporated, it is the host of graphics cards has not yet run on points , The board is not yet on electricity, self-test is not passed, there is no drop out of.Or should memory and power.Power is not connected to it, cpu fan the does not have a move, if moving the fan, then There may be a bad motherboard.Block independence for graphics should be able to check the card is not a good check and then check the
memory