monitor powers down right after start up

I have a new LG monitor that gives me a great picture to work with but after about three weeks of blissful viewing it decided that it would come on when I started my G5 but almost immediately went into powersaving (sleep?) mode. I find it hard to believe it to be the monitor so I'm thinking an internal problem with my sometimes over used G5. Any suggestions??
(This post is also in the 'newbies' area. MyBad.)