if your not worried about takin the berry apart, open the housing and clean out the stndby button they get stuck n dirty and sometimes needa be cleaned mine has the same problem i did it an hour ago =D
It's an old phone so I'm not worried about the warranty.
I opened up the case and it looked like one of the rubber pieces that holds the button was detached. That looked like the problem, but maybe that's how it is supposed to be.
Perhaps it is also possible that the contact point is not elevated enough? I need to get the right size screwdriver so I can open the rest of the case and get a better look at the button.
Try not to move the side rails, many have lost headphone Jack function after opening the case up. Also, make sure you don't get any lint or dust on your screen, or the inside of your lens or it will bug you to no end.
I need the mute/standby button, not the headphone jack! lol I'm willing to sacrifice the headphone jack which I never use for the mute button which I use every 5 minutes. The 8330's audio playback quality leaves a lot to be desired anyway and for headset I just use bluetooth. I cleaned the dust off with a microfiber cloth and 30% isopropyl alcohol solution. Worked like a charm.