Does anyone know how to Force shutdown htc one?

Hi cIsA, thanks for your considered response. I have good news and bad news. The bad news is that TWRP does indeed replace the fastboot screen and so I can confirm that after flashing TWRP onto the recovery partition, holding volume down and power boots you into the TWRP directly (recovery). The good news is that from within android itself (booting up the stock rom as normal), I did a factory reset and it removed this behavior!!! So holding down volume down and power, did bring me to the screen you show above. Once I got there, I could go to recovery which takes me to TWRP (as expected as factory reset doesnt replace the recovery.img) and because the factory reset rolled-back the automatic android updates, TWRP is working again, touch and everything! Am now able to flash the rom, and ADB/fastboot recognise the device as attached. Factory reset from WITHIN android OS was the key step to get that fastboot screen back and stop TWRP taking over. Hopefully this may assist someone else one day...thank you for your help and responses!

gunnyman said:

yep.
This is going to sound crazy but it works.
put phone under a bright light source
press and hold power
lights will eventually blink
phone will shut off

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- I just wanna say, you've completely saved my phone! My M8 was frozen in the camera app and had begun to overheat to an extreme extent (I had to put it in my fridge to cool it down, hah..), I'm quite sure the hardware would've been extremely damaged and probably would have made the device bricked, I never once thought of the ambient light sensor as a fix but it worked! Can't thank you enough lol this is why I love XDA :good:

Thank you so much you saved my life, i signed up just to thank you

reinaldo33897 said:

i read somewhere also that if you hold power button and volume up as well as volume down all at the same time for a few seconds when phone is frozen, it boots the phone like a pulling battery out reboot effect.

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Heisenberg23 said:

Thank you so much you saved my life, i signed up just to thank you

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Your wecome, that's what we are all here for, to help each other out. We do have those that are useless with their worthless comments but there are also those that truly enjoy helping others out. Nobody wants an expensive paperwight.

Power plus volume worked

Reinaldo33897 said:

I read somewhere also that if you hold power button and volume up as well as volume down all at the same time for a few seconds when phone is frozen, it boots the phone like a pulling battery out reboot effect.

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Thanks guys, I successfully rebooted the phone.
Holding down Volume Up plus Volume Down plus Power Buttons worked for HTC x9u. The light trick did not work. I suppose the florescent tube was not bright enough. Only the screen was frozen the phone was working normally. Just hold down the 3 keys if the light trick isn't working.