My computer monitor wont work - HP Pavilion a705w PC Desktop

Here's some tricks I would try...
1. Verify the monitor's power cord is plugged firmly into the wall outlet and the back of the monitor.
2. Verify the monitor cable is firmly connected to the computer and the monitor.
3. Verify that you have turned the monitor power switch on.
4. If the power light on the monitor is not on, test the wall outlet (plug in a light or something you know works).
5. If the power light on the monitor is not on, try a different power cord.
6. If the power light is on and yellow or orange or flashing, but nothing displays, or the display is incorrect, borrow a monitor from a friend. If that works, your monitor probably needs replaced.
7. Also, you could try your Monitor on a friend's computer. If it doesn't work, your monitor probably needs replaced. If it works properly on your friends computer, the problem may be with your computers video output port, motherboard video chip (or video card, if you have one), or drivers.
Good luck.

If your monitor shows a yellow light and it won't turn green, the problem most likely lies with the computer. If your computer is not sending a signal to the monitor, then you have a computer problem. One way to test this is to turn the monitor off and the computer off, too.
Turn the monitor on and if it is working, it should display a message telling you that there is no signal. If you see that message, you can assume the monitor is working. If you do see it, now turn on the computer and see if the message changes.
If you turn the monitor on and you get no message, you can assume the problem lies with the monitor itself.
If you have access to another monitor, hook that one up to test the computer output.

You can now either get the monitor fixed or the computer fixed, depending on which one is bad.

Will any USB device (keyboard, mouse, memory-stick) work when connected to your Dell monitor?
Will those USB devices (including your external disk-drive) work when _directly_ connected to your computer?

When the monitor detects no input "signal", it goes to "sleep", to consume less power.

Check that the "data" cable is securely connected to both the monitor and the VGA-output on the back of your computer.

Or, try connecting the monitor to a different computer, to see if the monitor works at all.

Or, try connecting a different monitor to your computer, to see if your computer's video-card is working correctly.

You need to check the power supply and see if the output voltage is correct, it should be written on the power supply board by the out put connector, if it is correct then it is possible that the inverter is bad.. I suspect a bad power supply.

is the PC started ?
can you try with different monitor

Please check with another monitor and make sure computer is working fine. Since CPU is running it may not be the issue with computer. After check with another monitor please contact your technician.

you might have to change the screen resolution on your "other" computer because it might no be a valid resolution for your monitor. Although you should see the screens when it boots up. You may also want to check if your monitor has an input button and select a different input.
Do other monitors work on your "other" computer?

I HAVE A 17 INCH MONITOR AND IT WONT POWER ON MY POWER WENT OUT AND NOW IT WONT POWER ON AFTER POWER WENT BACK ON