cannot use 'on/off' button and spontaneously turns off

long. long ago my on/off button at the upper right stopped working. no matter how hard I push it down it does not turn off the phone. I have used 'settings' as a work around for this.

however, over the course of several months my phone spontaneously turns off. at first it would do it witha 50% charge and only rarely. now it is a relatively common event. I may only have one app open, like the music, but it will just crap out even with over a 90% charge. I have seen many people post about this and most say to do a restore, but alas, because I cannot use the on/off button, this is not an option for me. buying a new phone is not an option for me right now either.

anyone?