I've had oddness with mine on occasion, sometimes my internet will just drop off, AT&T's DSL. When I diagnose the problem my computer comes back with a message saying that an internet/ethernet cable is not plugged in, when it is.
I've googled this problem and it seems other people have the same issue with AT&'s DSL service.... it randomly drops for random periods of time, anywhere from 5-10 minutes of half an hour plus.
Funny thing is my mom lives close by and also has AT&T DSL, and has no issues.