bought it second hand. any other solutions that i can do by my own? btw thanks
Without taking the phone apart, there isn't much you can do. Either the key itself isn't pressing down on the "plate" below It, thus making the phone not register the click. OR the plate below is corroded from some sort of damage.
As others have said, take it into your carrier and see if they can fix it, otherwise if you are a brave surgeon, you can take the keyboard out and try clean the inside, that MAY help.
Hope your issue gets resolved soon. I love my Q5 to bits