Vista 64 problems with Internet connection, Shut down and Programmes

Hi, apologies up front if this question has already been answered elsewhere on the Forums but I haven't been able to find it. I'm running Vista Ultimate 64 bit, recently I've been finding that after having any of my web browsers open for a period of time (ranging from 30 minutes to about 3 hours) they seem to lose connection. MSN and Vista are both still registering as connected but the browsers just give me the various page cannot be found messages. In order to reconnect I am having to restart my PC, but have found that Vista now refuses to shut down, it displays the rotating circle and then dose nothing. The system won't restart and now won't run any programmes either. I'm at a dead end and any help you guys can give would be brilliant.
Thanks TYorkshireman