So, otjandra:

You bought this from your friend, who didn't use it much, but didn't have any particular problems? Then, the minute you bought it, you started noticing it had the power on problem? I wonder why your friend didn't have that problem?

How long had your friend had it? You can still try to get Nokia to take it back. Maybe your friend should try to take it back, unless he got it from a friend too.