Here's how you can isolate the issue, in this case:
1).Restart your computer and listen carefully. Your monitor does not beep. If it sounds like your monitor is beeping, it is either speakers connected to the monitor or it is coming directly from the computer.
2).Check and make sure your monitor is fully connected to the computer and that it is plugged in. Try plugging the monitor as well as the computer into another outlet. Some beeping from your computer is normal but it may be confusing if you are not seeing video.
3).Open up the case on the computer by removing one of the side door panels. The side panel door is usually connected by two or more Phillips screws. Take out and reinstall the video card, memory and the processor, this is especially important if you have recently changed any of these pieces of hardware. Any one of these loose connections can prevent video from showing up and cause beep sounds that alert there is a problem.
4).Replace, the video card if nothing else works. You may have to replace, the memory, motherboard or CPU if nothing else works. Some piece of hardware is bad and it's just a matter of a process of elimination