EliteBook 2540P Dim Screen When Booted into (any) OS

[CredibleChris]

I have an old EliteBook 2540P laptop, circa 2012 – but it’s a 4-core i7 and, fitted with an SSD, it’s still a fast and capable machine. The small form factor and 1280x800 display suit me well, and it’s easily my favourite laptop I’ve ever owned. The display brightness isn’t the best, but using mains power it’s adequate.  

However, the display has gone dim – as if set to 50% brightness, even when  explicitly configured in Win10 to 100%.

Googling around, I found this support page https://support.hp.com/th-en/document/c00832191 and started following the steps (though not in order). On two occasions I actually thought I’d fixed it – I got the display to return to full brightness. (1) After doing a hard reset for the first time and (2) After updating the BIOS to the lasts available. In both cases, at the next boot it went back to dim operation.  

Frustratingly, the last step described in the support page above [Step 6: Check the display before Windows opens] doesn’t have a solution ……and it’s 100% obvious that the display is working during BIOS setup. It’s only when an OS is booted that the problem occurs. True for Windows booting from the HDD, also Linux Mint booted from a Live DVD.  

I’ve run out of things to try – anyone got any further ideas?

Thanks

[CredibleChris · Accepted solution]

For completeness.....

....the issue went away as inexplicably as it appeared.

After a Windows Update episode, the mandatory reboot took place, and I was back to full screen brightness - I was left with the feeling of "well, that's nice - but after I next power down or reboot, it'll be back to crummy dim display mode"

Except that it didn't. Now been running normally for 5 or 6 weeks, many power cycles, many Windows Updates

My favourite ancient (but still very fast and useful) laptop refuses to die.