When I have this problem, this is what I do: first, get your wireless password or share key and write it down so you have that with you (most of these things are caps sensitive, so keep that in mind)
Then right lick on the annoying triangle. Don’t troubleshoot, go to the network and sharing center. Now look for an option called “manage wireless networks” or “wireless network manager” There should be a list with your wifi in it. Find your wifi, click on it, and tell the computer to forget it.
The annoying triangle should be gone and there should now be like an asterisk — wireless networks are available.
Now all you have to do is click connect on your wifi and enter the password or share key. This usually solves my problems (for a while)