Weird WiFi issue!?

Just got my first Mac, MBP 13". My weird wifi problem is that I managed to get my link sys router setup unsecured. That was a major pain as I have comcast and had to clone my MAC address and mess with it for 2 days. NOW, I'm trying to set up security and as soon as I turn on WPA/2 or whatever, my router completely disappears as if it doesn't exist, no router setup, no internet...nothing! What's up with that? I'm using a link sys wrt110. I'm thinking about getting an airport exp but I hear it doesn't have the clone MAC address feature so It may not work with my comcast, but that's a different story. Anyway, the security issue, why does turning it on blow my whole setup to smithereens???