Audio Only Works Through Headset

Since upgrading our Fujitsu Siemens Amilo PI1505 to Windows 7 in the past few days I've only been able to get sound through a headset and not through the speakers. Not particularly having a clue what to do I've tried installing the original audio drivers but can't do so as Windows tells me that more up to date drivers are already installed.

Any ideas on how to resolve this problem and if indeed it is a driver issue any ideas how I can get the old driver to replace the new without Windows reinstalling the latest ones on Restart.