Got me stumped - and I do this every day!

Get it going again. Instead of browsing the internet, connect another computer to the same router, and try copying a large file from the other computer to this one.

It sounds more like the network adapter in the laptop has given up, or is throwing its toys out of the pram because it doesn't like the router. It does happen occasionally - one of our HP servers at work refused to talk to a Netgear switch. Worked fine with a different switch though.

Check that the pins in the network socket on the laptop aren't twisted and shorting each other.