So that laptop has this video config:
•Dual NVIDIA GeForce 8600M GT graphics with NVIDIA SLI
RGB, HDMI, TV-out (S-video)
What OS? If Win7 try Windows Key + P a couple times pausing for it to switch the display.
Is this a clean install using the OS install disk, or a factory recovery partition or disk?
Have you tried all 3 outputs - including TV?
Have you tried special function buttons to switch the display output? These buttons require you to hold down a special function key (FN) and a numeric (1,2,3..) or function key (F1, F2...) to do things like mute audio or switch to an external display.
Have you looked in the BIOS? Some BIOS have display settings for the external output such as clone or expansion.
You could also manually apply the registry settings necessary for the proper display setup. This would require using the console from the OS install disk to edit the registry and finding those settings from someone with the same graphics driver version.