|"I talked with HP tech support and the tech guy said..."|
These days, you may have been talking to some guy in a India, or in any case to some support guy who may or may not be competent.
It's a LOT more likely that one of these things is what is wrong than there's something wrong with a graphics adapter that produces a perfect display on an external monitor...
- the wiring between the base and the display is damaged due to wear, usually right where it passes through the hinge area.
Common after the laptop has been used a lot. Relatively cheap to fix.
Symptoms: The display may have been working when the lid was in certain positions, not working when it was in other positions, for a while before it wouldn't work at all.
- or - the backlight has burnt out in the display
- or - the voltage inverter that provides high voltage to the backlight has failed (it's usually inside the lid under the display)
Both are common after the laptop has been used a lot, or if the laptop has been dropped. The backlight is cheap but must be expertly replaced - most technicians get a replacement display assembly instead of doing that. The voltage inverter is cheap and easy to replace, but usually it's the backlight that has failed.
Symptoms: The display has had an overall colored tint for a while before there was no video at all. Then the display was normal brightess for a short time after booting, then it went black and stayed black. After the display went black, if the brightness is/was increased all the way, you may see / have seen a very faint image, sometimes.
Did he drop the laptop, or spill liquid on it. ??
Those things are the most frequent reason a laptop malfunctions such that major parts need to be replaced.
Have him take it to a laptop repair place that is certified to work on HP computers to analyze what is wrong.