Cannot access certain websites on any web browser

Recently, for the last month or two, my mac won't let me look at certain websites. (i.e apple.com, hulu.com, some yahoo.com sites.) Cannot find a solution on any forums yet that work for me. The internet works fine on the other computers in the house and I can access those sites with no problems. I have snow leopard on my Macmini, and I tried reinstalling it and the websites worked ONE time, then if I closed the browser the sites would come up with the error, cannot connect to the internet. Or in the case of the Hulu site, show text only with no formatting. I also tried reinstalling Java, and it did the same thing, would let me see the website once and then not again. Not sure what else I can try. Does anyone have any suggestions? Is there some update i have not installed yet that does not come up in my updates? Thanks for all help.