Power On/Off Button

Is there a way to know if the power button on my iBook is the problem of if it's something more serious? Computer stopped working and had problems with the power button in the past. Was in the middle of using it when the screen blacked out came back on then went dark again - no power at all now. Have already replaced the power cord so I know that is not the problem. When I push down the power button it doesn't feel like it is going in all of the way. Any suggestions?