AC1200 EX6150v2 WiFi Range Extender connection problems

I have a AC1200 Model EX6150v2 WiFi extender which has been working OK for the past 4 weeks connected to Surface laptop/tablet, Sony Smart TV and Samsung Note3. Connection lost for no reason 2 days ago. Have reset extender and strong signal showing (as previously). When I input Security Code comes up with secured but no internet on Surface and TV but OK on phone. Have checked internet service and modem with ISP - all good and no recent firmware updates etc. Message on TV is :failed - plse refer to the instruction manual supplied by your ISP. and retry Network Setup after configuring the Acct Settings PPPoE of your modem. Reluctant to make any changes as nothing has changed except extender stopped working and shows same strong signal as previously. Any help appreciated - Thanx