Another thought, maybe the router needs to be rebooted, we had storm weather here yesterday and even though I'd turned off the computers when the thunder and lightning started I didn't turn off the router.
We lost power a couple of times and when everything was fairly calm the computers went back on but my husband complained he couldn't connect, his machine is wireless and XP I'm wired and Vista
Looking at the router it's lights were on but the WLAN light which is usually blinking was steady along with the power and ADSL lights, I turned off the router waited a few seconds then turned it back on and everything was back to normal
Don't know if it would help but it was a thought on my part