Computer problem

My computer is (once again) dragging itself along this morning. In frustration I finally switched the whole thing off and on and now it tells me I have an error ''the host 'pop.skynet.be' could not be found. Please verify....' Have checked the settings as far as I know how. Cant now download mail or get on internet. Wireless is working. Can get online on my laptop. Please help before I go mad!
Thanks