I've been following this thread with interest as I have been having a similar problem with my wireless enabled laptop. As it's not the fastest machine in the world, I tend to close the lid to put it into standby mode if I'm not using it for a little while. Normally opening it up again brings everything backup and running, but if left for an hour or more the wireless connection refuses to work, even though all the indications are normal. Even letting Windows "Repair" it makes no difference. Shutting down and re-starting is the only thing that works. The link provided by Albert Square suggests the "Wireless Zero Configuration Service" may be the culprit. Next time this happens I will try disabling and then re-enabling to see if this solves it.
Thanks.