webserver down, cant find reasons

[peman]

This morning our webserver was down for some reason. when surfing in to some webpage on the server or the admin controlpanel it showed "Internet Explorer cannot display the webpage", i tried to find the error logs, cant find them, which error logs am i supposed to read to see what´s happening with the server?

I first tried to restart apache2, didnt work so I just rebooted the server and after that it was up and running again, this is the second time that it has happen but last time was a couple of months ago, i just wanna know whats going on.

Help appriciated