My Lumia 520 had a similar problem. I could switch on and off but couldn't open the lock(pressing the button once). Sometimes it would works but sometimes it wouldn't . So I got the button replaced and still no success, it was just like earlier. So here's what you should do- after getting the button replaced if it still doesn't work, do a hard reset of the phone and it should work. It worked for me :). Hope this helps.h
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My Lumia 520 had a similar problem. I could switch on and off but couldn't open the lock(pressing the button once). Sometimes it would work but sometimes it wouldn't . So I got the button replaced and still no success, it was just like earlier. So here's what you should do- after getting the button replaced if it still doesn't work, do a hard reset of the phone and it should work. It worked for me :). Hope this helps.h
My Lumia 520 had a similar problem. I could switch on and off but couldn't open the lock(pressing the button once). Sometimes it would works but sometimes it wouldn't . So I got the button replaced and still no success, it was just like earlier. So here's what you should do- after getting the button replaced if it still doesn't work, do a hard reset of the phone and it should work. It worked for me :). Hope this helps.h