Too many possibilities, including combinations of problems.
Ah, one question, if he had trouble with all three browsers, do all three use same dns file? Just asking for future reference incase someone should encounter this issue. Seems like all three browsers were affected by a single problem. Good call on it not going to the right address.
Dns issues are a bit out of my limited knowledge range though. But good to know for future reference. Always a good idea to check if other browsers are affected too, that narrows down the issue some