19LA20Q 19" the owners manual was accidentally tossed out and we don't know how to hook it up as an additional computor monitor .... do we need special cables etc.

Kindly type your model number followed by 'operation manual' in google search engine. You will find a number of websites providing free manual. Just download it and follow the instructions there.

Hook up the monitor to a working desktop computer. If you still don't get video or lights to come on then the Monitor is dead and would need to be replaced. You can also try anotherworking monitor on your desktop to make sure its not an issue with the computer.

Try SAMSUNG website and
http://tv.manualsonline.com/homepage/
www.retrevo.com
http://safemanuals.com/user-guide-instructions-owner-manual
http://www.manualbookdownload.com

mmarcen2000, If warranty with Samsung not valid option, you or someone will need to fix it!! IT WILL NOT FIX ITSELF!!! Your unit may have one or two things wrong that are a common problem with LCD monitors of ALL BRANDS. Contact Samsung to see if they have a CASH+OLD unit swapout program in effect for your model!!! If DIY is an option you would prefer to do, then check on YOUTUBE for videos that deal with "LCD monitor disassembly" and LCD monitor repair" . Lots of "BLACK SCREEN" lcd owners have done the repairs needed to refurbish their monitors to "working" status for less than $10 in parts. Your monitor's symptom is common to a possible "THERMALLY INTERMITTANT COMPONENT SOLDER CONNECTION" or "BAD, SWOLLEN, LEAKY" electrolytic filter capacitors. You will need to inspect for both if you decide on DIY fix. Do an additional comment to your above post to let us know your plan of action after reading some of my other responses to BLACK SCREEN owners. Approximately 98 percent of my responses deal with symptom of BLACK screen. Also visit other websites listed in those responses. Good luck. 12fixlouie

I suggest these tests and in this order.
1. trying a new VGA or DVI cable. Fixed it? If yes then your old cable is damaged toss it out. If no try step two.
2. Hook it up to a new computer. Fixed it? If Yes Your graphics card on the first computer may need to be replaced If No you likely have hardware damage in the monitor which will need to be repaired by a technician. If this is the case I recommend buying a new monitor the cost for repair is likely almost as much as a new monitor.

You cannot use a PC on that model. Send me your e-mail address and I will forward the owners manual to you. It explains it on page 19.

i found the users manual

I think that monitor might have been retired before you bought it; the white screen says that the backlight is working but the pixels are not being controlled by video so either the video cable is trashed or the input electronics are no longer functional.
You might try the following:
Go to the Control Panel, System, Monitor and delete the monitor listed. Then, with the monitor connected and on, reboot the PC to force Win to 'find' the monitor and install a fresh copy of the driver for it.
If that doesn't work, you may just have a paper weight.    

Thats because if you look in the owner's manual, it declares the fact that it will only broadcast sound from hdmi to monitor not speakers. For sound out of speakers need to connect additional audio cable.

Button on the bottom back base raises and lowers, if not low enough then you can remove the base. removal button is back and center of monitor.
of course you will have to deal with a way to mount it then.