Yes, the non-response of the Metro Tiles is due to the two AV running at the same time. Generally, this is not good; you only need one.
Defender isn't too bad, but AVG and Avast, both free, are better. . Depending on who rates them, one or the other is rated the best. I believe many AV programs will automatically disable Defender when they install. To make sure, type in Defender on the Start Screen and make sure it's off. I don't know how NOD32 rates. I have seen mention of incompatibility with Win 8.
