power button problems

Have you tried taking the phone apart to see if there is some lint or something stuck under the button causing it to now make a connection?  I know there are a few you tube videos that walk through the disassembly of a Cappy.

Other than that, are you still covered under the manufacturer's warranty or have insurance on the phone?  If still under manuf. warranty, you could try and get them to fix it but you would have to send it to them (and make sure that you return it to stock before that: ROM, battery, unrooted, etc otherwise they may say that you voided the warranty on it).  Or file an insurance claim on the phone and get it replaced (note: replacement phone may be a 'refurbished' phone and not a completely NEW, unused phone.)