To me this is a hardware problem.
Let's diagnose, and see Shunka_Reid.
Connect a VGA monitor to the laptop.
A) Laptop OFF, monitor OFF, connect a VGA monitor to the VGA port, on the laptop.http://support.gateway.com/s/notebook/2009/gateway/nv/NV78/NV78lv.shtml
Number 3 - External VGA display port
General example of VGA connector (port), and VGA cable,http://en.wikipedia.org/wiki/VGA_Connector
Scroll down a little for the VGA cable example.
You can use a CRT type of monitor, (Looks like a small TV), or a flat LCD screen monitor if it has a VGA cable.
General example of a CRT type of monitor,http://www.wisegeek.org/what-is-a-crt-monitor.htm
B) Turn the monitor on. If a CRT type allow it to warm up.
Turn the laptop on.
By factory default settings, the display should show on the external VGA monitor.
There are at least 3 display options available;
1) Internal monitor of laptop ONLY
2) Internal monitor of laptop AND external VGA monitor.
3) External VGA monitor ONLY.
Press, and hold the Fn key down, and at the SAME time tap once on the F4 key.
The F4 key is the Display Toggle-Over key.
Hold the Fn key down again, and tap on the F4 key once more.
Do you get a good display on the external VGA monitor?
Post back in a Comment.
Also, has the laptop ever been cleaned on the Inside, to your knowledge?