Monitor is black and diode doesn't light too- it's black.

Remove the RAM and start, see if it beeps and/or shows something on the screen. Try with the external screen too.
Let me know how it goes
Cheers

What you do is power off the machine, and disconnect the negative battery cable. Put a test light or volt meter between the battery negative terminal and the disconnected negative battery cable.

You will likely have a light or voltage reading...Then you start disconnecting things....I suggest the alternator.

When you have the correct component disconnected and the test light or volt meter shows no current.

If this component is the alternator, they have diode sets inside (or somewhere else in the charging circuit) Typically one diode fails and this causes the draw that you describe. The system often still charges, but at a slightly lower capacity with the failed diode.

Doc

• Nothing is more annoying than a monitor that refuses to turn on. Make sure your Acer monitor is plugged in to a functioning outlet. If it's plugged into a power strip, try replacing it with a new one or moving the plug to a different outlet. Ensure that both ends of the power cable are plugged in firmly and securely, and that the connection to the monitor is not loose.
  

Cable Issues

• Your Acer LCD monitor will usually accept DVI and VGA inputs. If you have an older computer, a VGA cable should work fine. If it doesn't have a VGA port, you'll need to obtain an inexpensive DVI to VGA adapter at your local computer store. A DVI cable, however, is compatible with most modern computers and offers superior picture quality over VGA. Make sure you're using the cable that's compatible with your system, and that you have the proper conversion adapter, if necessary.
  

It's getting power, it's just not getting signal from the data cable. The cord that connects to the monitor, (not the power) is typically the reason it is going into standby mode. This can also happen if your graphics card driver is missing on your operating system, but you said you tried the monitor on another machine, so I narrowing it down to most likely be the data cable. Try another cable.

I switch on my PC, ensuring that all cables, leads and power supplies are connected properly. The tower powers up no problems at all. I switch the screen on, the green led lights up, the screen is completely black. A blue box appears centrally on the screen with the text 'power saving mode'. The green led light turns amber and then the screen just goes black.

Please don't suggest going to control panel, as I can't get that far.

PLEASE PLEASE CAN ANYONE SUGGEST ANYTHING give me

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

Check to see if there is more than one 15-pin monitor connection on the back of your computer. If there is, try plugging the video cable into the other one.

Is this a new monitor? Was it working before this? Does your computer sound like it is starting up normally?

Did monitor work's on another pc?

If YESS so u need to change ur VGA