<!-- from fixya rte -->Monitor not working when plugged into laptop - Envision Computers & Internet

Plug in another monitor on the monitor output - if that monitor works then the problem lies with the laptop display. If the external monitor does not work also then the anomaly lies with the video circuits of your laptop. In either case , repair is expensive and not cost effective - better off just getting another computer.

You should have a video plug on the side of your laptop. It might be a 9 pin plug or a 15 pin plug. You can attach an external monitor or LCD monitor to this plug. If the green line displays on the external monitor then your video circuit on your laptop is faulty. If the line is not present on external display then your laptop LCD display panel is defective.

Unfortunately..your display may be shot...Is it a Compaq Presario? These laptops have a history of display problems...I have a Compaq Presario R3000 and the display is showing a reddish color in the left bottom corner of the screen and my brother had a similar problem with a Compaq laptop where the monitor stopped working....Unfortunately it would cost more to replace the monitor than to buy an Apple MacBook...
You can buy a cable and attach the laptop to a desktop monitor and it will work although you will lose the mobility of the laptop which is what makes a laptop so appealing.
If your laptop has a NVidia graphics card you can go to display in control panel and set it up to use Plug & Play Monitor but you may need to use safe mode or you wont be able to see anything because your screen doesn't work....You might get lucky and when you plug in the cable (just like you would to attach a PC tower to a monitor), it will work and you will be able to make the monitor the dominant screen.

There is often a function monitor key on the laptop, located near the F7 key area, the icon looks like a monitor on|off and is typically in blue. this key is to be used in combination with the Fn key to enable, disable the external monitor or enable both monitors or just the laptop. Press the key combination until your laptop panel lights up while the monitor is plugged in. Now check your extenal monitor refresh rate and resolution slider settings by right clicking on your desktop go to properties / video settings. (please note monitor settings are under advanced). You should see two monitors in there now. use "identify" button so you know which one to work with. on the external monitor settings, decrease (slide left the slider all the way). If you can set the monitor refresh to 60Htz. Lastly take a flashlight and check if you can see a shadow of your screen on the external monitor, if you can that means the backlight is not working and likely needs the inverter replaced. Hope that helps ! Cheers

Plug in an external monitor to your laptop, if you see an image on the external monitor then your laptop screen is bad. It could be the screen itself or a video inverter.

If you can't see an image on the external monitor, then your video card on the laptop may be damaged.

Good luck

-Carlos:

You don't write which operating system you use, but generally you should be able to choose where the sound output goes in the Sound Properties in Control Panel.
If however Sony decided to put some special software that does the thinking for you, and directs the sound output via the HDMI when connected, then you have to dig deeper...

Remove the battery and then put it back after about 5 mins. Plug it into mains and see if that solves it. Sometimes when laptops "hang" like this-removing the battery solves it.

On the laptop, you'll need to change the video mode so that the laptop knows to send the signal out the VGA port. The two common ways of doing this are to find the Function key and the monitor toggle button. It's usually one of the F-Keys at the top of the keyboard in combination with the Fn key at the bottom. Hold the Fn Key and press the toggle key a time or two with the external monitor connected. If this doesn't work, or you can't find the keys, leave the monitor connected and reboot the laptop. When the laptop boots up, the OS should detect the external monitor and automatically turn it on when the OS boots.

plug your external monitor cable to your laptop.
when you press Fn (hold Fn) and then press 5, for some model it give you choisee (display on lcd, lcd+monitor, monitor). to select the choisee you just press 5 again (you need to hold fn key)
if it still not working, plug your monitor to your laptop and boot.
ussually it work.

This problem is most likely to be caused by a bent or broken pin on the CRT video cable at the VGA connector, OR, this could also be caused by a damaged VGA connector on the back of the laptop. If neither VGA connector is at fault, the problem could be caused a damaged (kinked) CRT data cable, or internal damage to the VGA connector on the back of the laptop, though I suspect the problem is more likely to be external, and you probably won't have to disassemble the laptop to locate the culprit...