This must be a IIS bug.
When the CPU usage is 0% I can access the server by Terminal Service... everything works but IIS.
Nothing in event viewer... just a warning about SMTP... failure delivering..
Did you see here:
http://www.patroni.brturbo.com/
This show what happening... the server is working fine and stop to answer.... it doesnīt become slow before to stop... it just stop... and come back.. like this pictures showed...