Are you being asked to install the driver again?
What version of Ubuntu are you running?
Some computers have a hardware switch that will physically turn on and off the wifi. Perhaps you did that? The program won't work if the hardware is physically turned off. (for me, I don't have that ability, it is software controled for my bluetooth).
When you click the preferences tab, what does it tell you in the driver information tab?
Do you get any messages that ti can't find the driver on starting the program?
Will do what I can to help you out with this.