unable to move screen to external monitor???

Hi,
I've had my Powerbook 15" (PB) since late July. I've always been able to shift the screen image from the PB to my external monitor(em) by starting both at the same time, then closing the screen on the PB, which also shuts off the image on the external monitor. By clicking the space bar on my Apple external keyboard, it reopened the em and I had my screen image. Actually, it started out that way today. All of a sudden, the only way I can use my em is by keeping the PB screen on and just dragging the image over which I don't want to do. If I close the PB lid now, I can do as above and receive a blue screen with the traditional OSX screen, but there is no actual screen image. I can't use the mouse on that screen and I can't bring anything up on it. I have to reboot to be able to see what's going on. I did do an OSX update last nite as recommended by some auto update on the OSX. It was OSX 10.2.8, but as I mentioned, it worked fine for about 4 hours today??? I did do a viral update with Virex 7 last nite??
What's up and how can I get my image back over to the em only like earlier??
Thanks.
Frank

Yoda,
I'm thinking too, that it is the update, but since I had it installed last nite and rebooted last nite, and all went well last nite and even well into today, for about 4 hours, I'm wondering if I did something stupidly simple to explain away the problem??

Frank