I have that trouble a lot. Site goes down comes back up and I can't access it for at least 48 hours. I do all the things recommended and even rang my ISP and they reset some stuff for me. I just can;t access *this* site from my computer but I can from another one. Guess it must be an ISP thing but this is the only site I have the problem with! At the moment I can't access from my own!
Drives me insane!
rach