Everything was working fine, then all of a sudden, there was no activity to one computer in the network. It says its connected, but I cant access websites, and the other computers in the network are fine.

I had a similar problem when I set up my network. It turned out that after 8 hours of trouble shooting that the firewall had been blocking every bit of data that went between the computers. The connection showed up as a healthy and fast, but like you said, no data was getting through. Check your firewall settings and see if that helps; it fixed my problem and could have saved me 8 hours if I had thought of it earlier.

Sometimes when one pc dies it is because the DHCP server is down and it was the first one to have its address expire, worth a check. If you can release all then renew you should be fine on this point.

try to release your ip and renew it... ipconfig/renew

IF you are on an intranet... or a secure working office environment.. check up your proxy server.. key it into your browser's proxy setting..

firewall is another thing... check your firewall settings..

yes and it also might be worth your while to check your encapsulation settings on the main/master PC. i had a similar error and it turned out to be that my MTU number was wrong:)