Odd (to me) problem with internet

Okay a couple of weeks ago a computer in this house stopped being able to connect to a website with a forum that someone uses a lot. It couldn't be reached on this computer either. Then about a week ago, I couldn't connect to eyesonff anymore from either computer. In the last few days each website has started connecting again, but then the first one stopped again.

Does anyone have any idea how this could happen, I don't see how it could be a settings thing, as it affects both computers, but I can't see why single websites would stop being reachable by a certain IP address either.

Thanks a lot :)

When the computers stop working, do they stop working for all sites, or just for one or two?
If it stops for all sites, and you're able to browse on your other PC, then you most likely need to set static IPs on each computer.

Also, what is the protocol (ie http/https/ftp etc.)?
Sometimes firmware upgrades can break access to https and ftp particularly.