laptop - FN key "stuck" and non-responsive on my Lenovo ThinkPad T450

My problem

The FN key on my Lenovo ThinkPad has been non-responsive since some time last year and is just showing this constant green light which never turn off except when the laptop is turned off. The cause of it getting "stuck" in such way is unknown, but I am almost certain it is not due to physical damage as everything else works perfectly fine.

(except my battery which may randomly switch states and turn my computer off at random times, but that's another issue.)

What I've tried

I have tried various solution on the internet, like for example trying different combinations also attempted to disable the FN key entirely but nothing works.
I also tried contacting Lenovo and looked up on their forums, but it seems they only offer to replace the whole keyboard which is not an option for me.

It is quite frustrating as it stops me from controlling my volume from the keyboard or access other shortcuts which forces me to go out of my current session and do it manually.

If you need any additional information, I'll be happy to provide. I'm mainly looking for what the cause of this could be and hopefully a solution for this and if anyone else has experienced something similar before with Lenovo Thinkpads.

Thank you in advance, any help is much appreciated.

Answer

I am almost certain it is not due to physical damage as everything else works perfectly fine.

It is often the case that an accumulation of detritus or a drop of liquid affects one key without affecting others.

If you suspect a OS/driver software issue, simply booting from a "rescue" CD or USB drive will disprove that.

The operation of the FN key is likely to be handled in firmware (or, in legacy terms, BIOS). You could check that at power-up to see if there are any available settings that might affect the usage of the FN key.

My guess is a hardware issue: - spilled food or drink; dead insects; discarded staples, simple mechanical failure from impact or overuse or defect etc. As a first step, it should be simple to remove two keycaps and inspect, compare and clean the mechanism.