Why can't I connect my Iphone 4 to our home Wifi?
A few years back I had a particular wireless access point that would often exhibit this behaviour. One or two devices wouldn't connect after some time (a few days, maybe a week). Rebooting it let everyone back on.


Try rebooting the access point.
Check for driver/firmware updates (access point and devices).
If you can, borrow or swap access points temporarily to see if its any better.


It seemed, in our case, to be a bug in the router, but never really figured out if it was randomly 'breaking' for certain clients/chipsets/etc or if it was something more consistent like a bug in the 802.11n compliance... in the end we replaced it and all was fine.