Why , does it not work as a pc monitor when it should, as it is hooked up correctly?

the problem,maybe the PSU the computer might not get enogh power.or you can allways clear CMOS and se if that helps.

You have three components which could be faulty: Computer, cable and monitor. Replace them one by one until you find out which one is giving you trouble:

1. Hook up a portable computer to the monitor, using the same cable
2. Same thing, only with a friend's cable that is known to work
3. Try using the cable to hook up a friend's computer and monitor
4. Take your monitor to your friend's house and see whether it works there
5. Try using any other source of image, check the back of your monitor to learn what else you can plug, other than a computer

Each combination you try will give you more information, until you have enough data to isolate the problem. It *could* be that your computer's resolution is not supported by the monitor, but I doubt it.

lets first check weather the vga cable is properly attached to the port.if ok, and still no video the fastest way is to hooked up your pc to the other monitor just to ensure if monitor issue. by the way does your pc has power indicator how about the fan in the power supply does it work?,you have to considered those things to isolate where the main cause came from.

because it doesn't receives any signal from the pc - check the video cable. If the cable is correctly plugged in at both ends then the pc is defective - test it starting with the video card.

First I would make sure the video out on your PC is working correctly. The best way to do this is by hooking your PC up to a different monitor to see if the second monitor operates correctly. If it does not then possibly you may have an issue with your video card. If you are interfacing to a laptop, make certain that you have the video out configured to output to an external monitor. This can be achieved through your computers control panel.
I also had a similar issue with one of my ViewSonic monitors and resolved it by completely unplugging the monitor from my PC and also for the electrical outlet. I let it sit for 5 or 10 minutes, hooked everything back up, restarted the computer and it corrected itself.
Hope this helps
Codebynite

if your PC works with a standard monitor, just make sure you select the correct input on your TV. No special software needed.

check to see if you have two ports in the back of your desktop, try the other one if you do. If not, there is most likely a loose connection.

You need to check the Format, either NTSC or PAL, USA = NTSC, Europe etc, PAL. Set this correctly.

You need to have the correct drivers for these monitors installed on the acer. You can boot in Safe Mode (Hit F8 key at boot-up) and the monitor should work. If that doesn't work, your video card may be shot.

It is hooked up correctly. just have no volume even when its turned up. check for speker open or loose wire or broken wire. check sound section in monitor.