My monitor keeps turning on and off automatically,...

CHECK IN BIOS MODE ,THIS PC NOT GOES TO STANDBY SO PROBLUM IN YOUR OS .FORMATE PC NOW CHECK .

What does the VOX switch do?
When the VOX function is active, both the LCD screen & Audio turn off and will automatically reactivate when there is
noise in the room being monitored (e.g. baby crying). This feature is useful at night so the light coming from the screen
doesn't bother you and also when running the MobiCam Ultra receiver on batteries since it will extend the life of the
batteries. Note: The VOX function will not work when batteries are low and you cannot change channels on the receiver in
the VOX mode

You can't even get into the BIOS. Hard drive failure?
Here's what the manual say's about black screen.

Verify that: The monitor cable is securely attached to the rear of the monitor and to the rear of the computer.
The monitor power cord is plugged into the monitor and into a working electrical outlet.
The monitor is turned on and the brightness and contrast controls are set correctly.
The voltage is set to the correct setting for your country.
The monitor signal cable is securely connected to the monitor and to the monitor connector on the computer
.Note: If your computer has two monitor connectors, verify that your monitor is connected to the one in the AGP option connector rather than the one in the rear of the system board.

If you can check the monitor by using another monitor.
I suspect hard drive failure. Keep me informed on what you tried and I'll keep checking to come up with solution.

1 MAKE SURE THE DATA CABLE IS CONNECTED TO THE CPU.
2 MAKE SURE TO TURN THE MONITOR ON.

I had the same problem with my eMachine t3418. Site advisor Micromend suggested changing the power supply to more wattage. Very much recommend doing that. I did but it didn't fix the problem. Micromend also advised trying a video card. I bought a cheap vid card and installed it. It worked. Apparently MY problem was in the motherboard and the vid card worked around that. Much cheaper than replacing the computer. I'm NOT a tech. Just sharing my experience with what worked for me. I you have a laptop or a friend does, hook your monitor to it to test that it's okay first though.

try to reset it to factory setting. First press ok then down arrow 7 time then ok one time next down one time then ok.
Hope this help you.

Try your monitor with another computer. If it's still a problem. This is the way how to examine what's wrong with your LCD monitors. Power on both CPU and monitor. After the monitor goes off, you check that you can see the image on the screen by shining a flashlight into the screen, not directly but find the best angle to the screen and take a look very closely. If you can see the icons or any image, there will be a minor problem. Like me, I can see window image using flashlight and check lamps inside. Some of them were broken and it is easily replaced. If you cannot see anything on the screen, there'll be some problems with inverter board. If you have soldering tool and want to fix it by yourself, check the caps first. It may cause this problem. Some caps might show leaking or burn spot on the board because of too high temp. If you don't have soldering tool, you better go get a technician to do so.

try pressing the buttons (with your monitor turned off) if they have allowances for switching (if it is a push button then each should be pressed slightly and you should feel that it switches through!) if you pressed it and felt hard ( like something was stuck) then the buttons might have misalligned from the switches on the board. do not open your monitor unless you have electronic servicing experience. other causes might be the monitor's sync. processing IC. it could be defective.

When the screen turns black again take a flashlight and shine it in the bottom left hand corner where the Windows Start button is located. If you can see a faint image then your back light is failing. If that?s not the case the next step would be to attach another monitor to your computer to see if the problem disappears. If it does that points to the monitor, if it doesn?t then we need to take a look at the computer itself. Let us know what you find out and please don?t forget to rate this posting.