The spring mech seizes,and the only way to overcome this is to get the switch out and free it off,but this entails a lot of dismantling,and unless you are keen,a lot of fiddling about.
You might be able to "bounce" the spring out of it's guide by simultaneously holding the button in while gently tapping it.
As mentioned above though,the tv is perfectly safe in standby,and uses hardly any current in this mode.
If you are uncomfortable leaving it powered though,you might like to try a "powersafer" device.
This connects to the mains,and you connect your tv to it.It's designed to remove mains power automatically when it senses low demand,ie standby mode.It also senses remote control commands to switch the power back on when needed.
n.b.check with the supplier that the device will function with B&O remote controls,as these use non standard frequencies.
Nick