My Acer has a little switch with a picture of a satelite dish (looks like that to me anyway) and everytime I've thought it hasn't connected it's been because this has been knocked off, it should have an orange light if it's on.
Worth a try, if it's something more complicated I'm sure someone will help.
My Toshiba is the same as 'learntojive' - a small slide switch on the bottom which easily accidentally disconnects the wireless, especially when you use it on your lap.
I know, I know, one is not supposed to use a laptop on one's lap.