01-03-2011 How do you fix the on/off buton on a Sony Ericsson QuickShare?

It is a few years old now. Sorry I dont have anymore detail as to the model but the phone is currently off and will not turn on. The button ( small circular, on top of phone ) moves freely but is ineffective. Phone is charged and ready to go if I could just get it to turn on. Any suggestions gratefully received.