Our ISP had a major power failure yesterday evening (utc time) and this caused our site, among thousands of others, to be unreachable for some hours. Problems seem to be solved now and everything is back to normal.
According to the information provided some 1500 servers with 8000+ sites were down from yesterday evening 16utc onwards to approx 00-03utc, depending on the order they were restored. Reason for the failure was in a faulty electrical circuit in the power system of the server rooms. When it broke down it prevented UPS systems working and eventually when the UPS batteries ran out the servers started to go down.
So nothing we could have done but all in all a very major and unfortunate failure.
Update: One of the three servers we operate one is even still down so our emails are not working at the moment but it should be restored today.