PLVZ2 Won't Lock onto Laptop Signal

Hi,
I have a Sanyo PLVZ2 projector which I have had connected to my laptop to watch a movie on before, and everything has been hunky dory. Recently I purchased a dvd player with a vga out socket and have tried that connector, along with it's component and s-vid. Thinking that none of them are up to the quality of the laptop, I went to re-try it to make a comparison to the player. Since I have re-connected it, the pj has trouble locking onto the signal, with the desktop image flashing on for a second and then off again, repeating this process constantly.
I just wondered if anyone has any ideas what the problem may be as I'm a little stumped?
Thanks in advance,
Dean.

 

Update:
Had some success, though not quite what I'm after! If I go into the display properties of my laptop, and the projector tab, I can get the signal to lock if I select a resolution of 800x600. This gives me an image that is larger than the screen (ie, when I move the mouse up or down on the page on the laptop, the pj image scrolls itself up or down.
When I change the resolution back to 1024x768, the flashing syndrome re-occurs.
Stumped!
Dean.