Just recently I was faced with the problem of not having any internet access, and it happened randomly with no reason at all. I run Window's 7 64 bit on a computer I've owned over a year now and this is the first time happening. The internet sign on the toolbar at the bottom right of the screen shows the bars of connectivity I have to my home network (Linksys, I believe.. Wireless-G?) as four bars, but I have that dreaded yield sign, the yellow triangle with the "!" inside.
I have explored many options, unplugging my routers, running Windows diognostics (usually with no problem detected), I have done the ipconfig /flushdns and /release and /renew in cmd prompt, and went into control panel and adapter settings and checked to see if the ip and dns were automatic (they were) and I'm at a loss now. I even tried disabling my firewall. I don't think it could be my network card being that I AM connected to the network, just it says the network isn't connected to the internet.
Oh, and by the way, my laptop, xbox, phone, etc. all can connect to this network fine.
First thing I would do is check to make sure the wireless security is correct. I have been able to connect to a wireless router and had the yellow triangle and found out it was because I had the wrong security settings.
If everything seems ok, disable security at the router and on your wireless connection and see if it makes any difference. If it does, you know it is a security issue and you need to setup the security again making sure everything matches.