I do not know what has caused this but my websites have been down for 2+ days now and I cannot connect via SSH or FTP either.
The only way to get signs of life from my server is to reboot it via the members area of my provider, this sorts everything out very briefly before everything returns to it's broken state!
I didn't make any configuration changes so unsure what may have caused this. I do however have my ubuntu set to automatically download the daily updates.