My 650VA APC back ups power button seems to be working weird now. If it switch it off, I cant switch it on no matter how many times i keep pressing the button. Suddenly it will start on the nth time. Then i cant switch it off if i press the button 4-5 times. I've left it on now. Is there a way to get replacement button or just leave the ups as is? The thing is 8+ years old now. Button probably wore down.