How can I fix my Phillips Iqon pc intermittent sound problem?

I have a Phillips Iqon pc which has an intermittent sound problem. Sometimes when switched on, the sound works, more often than not, it doesn't work. I have tried swopping speakers in case they were the problem but its not the speakers. I have had a new card put in for the speakers to connect to but still no sound. I would be grateful for any advice on the way forward.