O2 XDA IIs - Speaker Off, Call Recieve Failure

I am using O2 XDA IIs, the recent problem I am facing is that the speaker is off, it rings for each the in-coming call but after pushing the receive button, I can not hear any sound coming in so I can not communicate to the caller. But if I use the headset, I can hear the caller and communicate. The outer speaker usually is on everytime I push and hold the receive button for a few seconds so I can hear the caller's voice coming out from the speaker but now is inactive. Anyone know what's the problem with my pda? Thanks...Andy