macbook screen failed

Hi all, I have a question, hope some one has an answer for me. My macbook backlighting started shutting off intermittently then failed completely. I now have a new macbook Pro but I wanted to use the macbook with a monitor. I got a dell 15 pin 18" flat screen monitor and an apple mini DVI to VGA adapter and connected my mac to the monitor. If my macbook is asleep for a while the screen will light when I open it as will the monitor for a brief moment. Then they both go to black. I can see a ghost of the screen image in the black of the macbook, it's just not back lit. I thought if the macbook screen was the problem the connection to a monitor would work just like when I would hook it up to my tv. When I have the macbook hooked up to the tv it works? Any ideas whats going on?
Thanks
Patrick