Sorry this is so long, but it's detailed.
I have been attempting to fix a Dell Inspiron 1525 that my grandmother spilled a glass of wine on. When I got the machine, it did nothing. It would charge the battery, but that was all. If you pressed the power button, you'd hear it spin up for half a second then stop. I found a parts machine craigslist and picked it up. The parts machine actually worked well, but had a few issues. A missing ESC key, no battery/charger and the fan was janky. The fan worked, but would only work for a little while before it would start whining and stop. The guy I bought it from repaired laptops and was just clearing out some excess stuff. He was worried about selling it to someone who was going to try and use it full time and was happy to sell it to me knowing I was going to rip it apart and use it for parts. I verified that it worked before buying it, it booted fast and had a clean install of Win7.
First, I swapped hard drives (Grandma's was also Win7) and booted the parts machine to verify the HDD worked and it did. So I stripped both machines down and started to rebuild using the best parts from both machines. After getting it all built back up, I powered up the machine and it booted just fine. The one thing I noticed was that the screen didn't come on immediately, but did as the startup sound played. I had no problems, played around with it to make sure all the buttons and functions were working and everything checked out. I turned it off to finish snapping some of the last parts off like the hinge panel with the plastic power button actuator and button up the last little bits and pieces. Then I turned it back on and this time, the screen wouldn't come up. Windows booted and played the startup sound, but I got not display.
This morning, I unplugged the LCD and plugged in the other LCD. Same thing. Blank screen. Machine is still booting fine, but no screen.
So I hooked up an external monitor and it popped up no problem. Device manager shows no issues. Pressing FN-F8 to switch from external to LCD just flashes the external. It doesn't turn on the LCD.
Then something weird happened. The machine went in to hibernation. I noticed it because just before it did, the LCD came on. When I woke it up from hibernation, only the external worked again. So I sat and watched it diligently waiting for it to hibernate again. When it did, the LCD came on just before going in to hibernation and I moved the mouse quickly to try and prevent it from hibernating. When I did this, I now had both screens and could even press FN-F8 to switch back and forth between them. I switched to the LCD and rebooted the machine to see if it would remember the setting. But when it came up, it was blank again.
At this point, I decided to try the other hard drive that came with the parts machine and a fresh Win7 install. It behaves exactly the same. Doesn't recognize the LCD. Device manager reports no issues.
Booting to Bios doesn't reveal any issues that I can find.
But then I booted to the Built In Self Test. As soon as I pressed power while holding 'D', the screen lit up and started rotating through red, green, blue, black, and white screens. But as soon as I let go, it booted to windows and only to the external monitor.
I'm so frustrated trying to figure this out.
What I've not tried is using the HDMI port. I assume that the RGB connection uses the X3100 GPU? If so, I know it's working fine because it has no issue with the external monitor. I know the LCD is connected because the BIST works. Both Win7 instances behave the same, so I have a hard time thinking it's an OS issue.
The only thing I can think of is that the Display connector has an input pin that feeds information back to the motherboard that isn't working and that's why Windows isn't recognizing the LCD. But why does it turn it on just before hibernating?