Devices not working when booting up

Hello,

Im having a problem with my devices ( mouse, keyboard, monitor etc.). Very rarely do my devices work or start up when I turn my pc on. The only thing that is turned on and runnning is my pc. I have checked to see if everything is properly attached including the devices listed above. Is there something wrong with my pc or monitor or any of my devices? (I think that it is my pc because it's either all devices work, or they all don't work at the same time. They never differ from each other. I also don't have access to starting my computer because even if it occasionally starts up with the other devices, I have another problem, but I can deal with that if I can get my pc to start up) thanks a bunch ;)