It must be a conspiracy: my Billion G has run flawlessly for months, and chose yesterday to play silly beggars, too! Incredibly slow wireless, total re boot, fiddled for hours, re-set the WAN password, 10 minutes later it all came good for no accountable reason
Fingers crossed, all OK now.
Did you try a reset? Pin into the hole at the back (marked "reset") with power on. You'll have to input all your settings, but it may cover your fault.