Monitor shuts down after windows loads?

[ELI37]

My in-laws have a Dell Dimension 8200 series that they use for every day web browsing and so on. They upgraded their CRT to a KDS 19" lcd about a year ago. Last week they could not get the monitor to stay on for more than a few seconds after windows loads up. I went by and checked all the connections and blew any dust out of the case that was there. It still shuts down? I could turn it back on again and it stays on for 3-5 secs. then shuts off again.

Any ideas what to check?