I've got an HP DV5-1125nr with a backlight that seems to work when it pleases. This started about a month ago. An image is still present on the screen and it works with an external monitor. Incidentally, the display cable was replaced almost two years ago because it was worn, but this seems to be a different problem. Though the problem comes and goes, I have not yet been able to induce the problem myself, nor found out what restores backlight function. I have seen the backlight go out instantly or with a flicker.
Attempts to fix it:
The cable, inverter, and bulb have been tested and replaced and have not resolved the problem. Recently, when the backlight wasn't working, I removed the lid switch magnet and the backlight began working again, but when I closed the case back up it wasn't working anymore.
Other issues (Are they related?):
This laptop also experiences two other significant problems:
Sometimes, on boot, the caps lock and scroll lock lights blink indicating bios corruption failure, but after several attempts of manually shutting off the computer and then powering on again, the computer will successfully boot.
With no apparent cause, the computer will freeze with a crackle/pop. The screen will go black and lose all display, the wireless indicator light will change, and the caps lock light is not responsive. This also happens when unplugging AC power to run from the battery.
There are no other problems operating the computer once it boots correctly.
Other background info:
These problems started about a week or two after the computer was recently upgraded from Windows Vista to Windows 8. I recently updated the BIOS to the most recent version (from 2009), but the problems were not solved. It has an AMD processor and tends to run hot, sometimes as high as 70-90 C, but the incidence of problems does not correlate with temperature. The fan and heatsink are clear of dust. I own a multimeter.
Maybe there is heat damage to the motherboard? I have no idea at this point.
The backlight is completely functional but can go for hours or days without turning on. The computer sometimes has trouble booting and sometimes freezes as if something has shorted out.