Call up your cable company. If the only thing that changed was the ISP, then the problem is obviously with your new ISP.
FYI a warning about failing to resolve a hostname implies that your ISP is not providing reverse DNS capabilities on your IP. This may be a temporal issue, or it just might be the way the ISP decides to work. It also might just be a routing issue with that one IRC server. Either way, you need to contact your ISP to confirm the problem is on their end.
