Can you go onto the computer thats not playing and go to a cmd prompt. Either type it under run or type it into search programs.
Once you get the box up type "ipconfig -all > ip.txt"
Then do the same for one that works but use ip2.txt for the file name and open them using a text editor and copy and paste it back onto here.
I have a feeling the one that doesn't work has a fixed DNS server which is different to the rest.