When I switch on my computer a message comes up on my monitor 'signal cable not connected. also the keyboard and mouse have stopped working, I have tried another cable and monitor but to no avail. My computer is a desktop and it's only a couple of months old, before I call someone in I would like to know if there is a problem with the motherboard or the PSU, it was working fine before this problem, can someone come up with an answer please - Dave.
Did you install any new hardware recently like a video card? I had the no signal message when I installed a new video card since I set in the bios to use integrated video as primary rather than setting it to auto (switches to PCI-E if there is a new video card).
Also try taking the power cord out and holding the power button for something like a minute or two.