Is it possible that you, or someone in your household, has turned toe SSID Broadcast off on your router? Meaning that your router doesn't 'tell' wireless devices in it's proximity that they can connect to it..
I'd double check your router settings just to be sure
If that's not the case, go into the wireless settings on your laptop and manually input the SSID of your router, and it should find it.. if it doesn't, there may be something wrong with either the software you're using, the wireless card in your laptop, or your router.
I'd say it was the router. I had one that did this, it kept timing out so I could not pick it up. It may of reset itself somehow. I would double check all the connections are correct then change the channel of the router to 1, 6 or 11 if you can (You said it goes off and on again so try to do it quickly when its on!).
If you do not know how to do this or there is any other problems just post them!
Just a hint, check on the side of the laptop or in front of it. Sometimes they have switches that turn the wireless off, my sister did that a week ago.
Well other then basic trouble shooting and a total reset, you may have a bad NIC or something. Your next task is to find a wireless USB device and see if that works.
Generally, I don't update unless there is a problem. Try the update if there is one, and if not, try one of the USB adaptors. If that works, then you might need a PCMCIA one (goes in a slot in the side of your laptop) to replace the internal one.