why PsychPortAudio('Start', ... ...) takes so long

1
I am using psychtoolbox to develop some behavial experiment.

here is beginning of my code
=======================

triggerlevel = 0.05;
InitializePsychSound(1);
freq = 44100;
pahandle = PsychPortAudio('Open', [], 2, 2, freq, 2, [], 0.02);
PsychPortAudio('GetAudioData', pahandle, 5);
PsychPortAudio('Start', pahandle, 1, 0, 1);
Run_time = GetSecs;
max_RT_duration = 5;
fprintf('0 sec -- experiment start. \n');

... ...
... ...
=======================

When I run my program, most of the time, I have to wait at least 30 maybe 60 sec to get the display ''0 sec -- experiment start.'

Can anybody tell me what's wrong with the 'PsychPortAudio('Start', ... ...)', and why it takes so long? is there anything wrong with my parameter setting?

I am using PTB - 3 on windows xp, my computer is HP XW4600

Any advice is appreciated.

Simeon