reconnected router this afternoon (after being powered down and unplugged all night so nice and cool) exactly same problem so as a last resort reset the router using the reset button(held in for 10 secs all lights went out) and lo and behold all was ok again. So powering down didnt work but reset did. Now been up and running for an hour and all seems ok again.
And like i said it was the wireless connection to the router that was failing not my connection to the internet, connection to internet was fine. So now I have got connection back up have moved from mixed to g only and ch6 to channel 1. Will now wait and see if this stabalises connection.