Unable to connect to microsoft websites

Hello, when using my netgear DG834GT router i cant connect to msn, xbox.com sign in, windows update, windows live messenger and windows defender update(via firefox after working fine for over a year). Error codes for messenger 80048439, windows defender 0x80072ee2. However connecting via my old BT voyager 100 modem it all works fine. After googling the error codes i have changed the MTU setting in my router to 1500,1492,1458,1400 and then using SG TCP Optimizer and largest MTU and that came back with 1453 which didnt make any difference. I've reset the router and used the setup wizard, ran AVG, CCleaner, Windows defender ,Ad aware and spybot S&D but no joy. Thanks for any help.

 

Update, seem to have fixed it, changed the MTU setting to 1400 and used DRTCP as recomended on the netgear site for aol users. Must have been doing it wrong the first time. If i could ask though, how could it have stopped working in the first place without me changing any settings and the optimizer recomended 1453 so am i losing an performance etc? thanks again.