All One Series phoneshaving been facing this problem of QHSUSB_DLOAD where the phone is completely bricked and rendered unusable. It has been reported by many people that pressing Volume Up + Power instead of Volume Down + Power can be a deadly mistake...You have to send the phone to HTC and they will repair it but instead you could avoid this brick by being a tad bit careful and not pressing the Volume Up instead of Down...
This is just one case but it may also happen in other cases but this is easily avoidable unlike others which just happen out of the blue...This is one precaution which can help you.
SCENARIO 2: POTENTIAL BRICK!
Also if battery is extremely either switch it off or wait for it to switch off...Do Not REBOOT YOUR PHONE...That might just cause this above error as well....
SCENARIO 3: TOOOO LONG!
Do not hold your Vol Down +Power Down for toooo long like 10+seconds or it might cause a brick. IF it doesnt go to bootloader or if you are scared use this fastboot command: adb reboot bootloader or try the button combination again..
SCENARIO 4: STAY AWAY FROM ROM MANAGER
Please stick to the safe way of flashing by accessing recovery manually and refrain from the use of Rom Manager..It uses fakeflash which is potentially dangerous for most phones...
SCENARIO 5: THE UNPRECEDENTED ONE!
The above scenario just happens..It might have no proper explanation like it happened to someone while he was talking on the phone...etc
Fix for QHUSB-DLOAD issue
MOD,PLEASE MAKE THIS A STICKY!