Well my computer had one of those "Windows automatic updates" a day or so ago and now I have no sound on my computer at all.

If I go over where my volume control used to be, I get a message saying "No Audio output device is installed".

How do I install one, or get the one I used to have back?

If it makes a difference, I am using a Toshiba Laptop on Windows Vista.

try downloading a soundcard driver from here, that's what I would guess the problem is, however you do need to do a bit of research into what soundcard you have, as there are many different types of toshiba laptops as you can imagine.

My advice, find out the model of your laptop and do a google search "(laptop model) laptop sound card driver" and see what results that shows.

also see if the driver for your soundcard is here:

http://www.driverfiles.net/Sound-Cards/Toshiba/page,level2,221,7,resultpage1.html

other that do a system restore and then download that windows update again (could of just formatted in a dodgy way).