Monitor says no signal

This could be a multitude of things. Firstly, check the connections from your computer to your monitor, unplug them and plug them back in, make sure the thumb screws that connect your monitor to your computer and nice and tight but dont use a tool to tighten them, hand tight is good enough.
If that doesnt work, then check that your graphics car hasnt been unseated from its slot, TURN OFF THE POWER to your pc, open the case and look at the graphics card inside. Push it straight back against the slot and that might help.Try connecting the monitor to another computer, although I dont think its a monitor problem. or borrow a monitor from another computer and try it. If that doesnt help then you can try a different graphics card, if you dont have one they are readily available from most major electorincs stores, or even most supermarkets with an electronics dept. Now if you do all this and it doesnt fix it then you will need to find a tech to have a look at it, Like I said at the beggining it could be a multitude of sins, a hardware error stopping the computer from booting and that requires a little technical knowledge