dcdiag looks at the event logs, and if the event logs have errors, they get repeated by dcdiag.
So for your first, it is saying that there is a significant error in your event logs with the id 15100 and was generated on 6/25 at 8:30:08
It even says "event log = System" so you know which event log to look in.
fire up the event viewer, go to the system event log. Scroll down to the point in time that dcdiag reported the error, and see if it is a transient error or a reoccuring one.
....rinse and repeat for the second dcdiag error.