System Event Log

I have a Guest account set up but my friend could not get into it. I am the
Administrator. I received a message on my desktop saying there was a 'sens
service' problem, that Windows could not access System Event Notification
Service and that as the administrator I was to look in the System Event Log.
The Guest account does not open. Why is this? and how do I go about fixing
the problem so that I can use the Guest account.