Something I have noticed, and thought others could benefit from.
I have an IS DSL account, and when I am soft-capped, Skype has difficulty connecting. When this happens, Skype also tries to listen on port 80 - and this kills Apache startup. Now, I am not sure why this happens, but is does!
Three suggestions here -
stop skype and start it once Apache has started
change skype so it does not use port 80
(#4 - don't get capped! )