Why does my banking site keep telling me system unavailable? Its driving me nuts!

I have been going to a banking web site for almost a year now. The past 3 weeks or so, I cannot get it to come up. I type the same address as alway, and it tells me system unavailable-contact customer service. I have contacted customer service twice now. They can get into my account on their end and say I should have no problem.
What is the problem? How can I fix this? It is makin me nuts!