that isn't a monitor problem. The monitor is giving you the notice, I assume, which means it is working.
The boot device (where the computer gets told the system operating instructions) is usually the hard drive (the error even says so). Having a "no boot device" warning is a pretty scary thing, because it means that your operating system cannot be read, and presumably you used to have one, so if it cannot be read now, that means something seriously wrong with your computer.
Presumably, the hard drive is corrupt and operating system cannot be read. This can be fixed, but it is not a simple thing for someone not familiar with computers.
The usual way to go about testing for where the problem lies is to boot the computer with a cd containing the operating system, and then test from there. Don't do any formatting or wiping of any memory until you figure out the problem, or you will lose everything on the hard drive, and that ain't no fun at all.
Unless you have already done that and this is why there is no operating system. I hope not for your sake.