very slow connection, new tablet says "connected" then "can't connect to internet"

I have a wndr600 v3 which I bought on Craigslist. this is my first time setting up a router. I managed to get a signal, get my macbook pro connected and find my way to the routerlogin.net website. It seemed to be connected there at a decent speed. When I went to other websites, the speed was horribly slow.

what to do, who to call?

then I turned on my brand new tablet and it fired up, connected to the internet via my wifi and then took me to a terms and conditions page, after that it said "can't connect to the internet"

I'm guessing somehow the speed is just so slow. Are there any settings I can change to make this a faster connection or did I just buy a **bleep**ty router?

thanks in advance

betsy