MacBook not connecting to WiFi network or connecting and saying "No Internet connecti

[0dev]

My iPhone and iPad are working fine on my WiFi network, but for some reason, my 2007 MacBook has decided it isn't connecting anymore, and when I do get it to connect, it says "Alert: no internet connection".

This has never happened before and I've had the laptop since new and the router at least two years.

I've tried repairing the permissions and rebooting, neither of which have had any effect.

The laptop's running on a recently installed copy of OS X Snow Leopard with all the updates.

I have not installed anything prior to this issue cropping up.

Any help? Thanks in advance.

 

[0dev]

Just tried restarting the router, that made no difference either.

I also notice in Activity Monitor, "ntpd", "launchd", and "mdworker" are running twice.