Optiplex 760 SSF Audio Issues

I first loaded the unit about 1½ years ago using a Memory Stick from Dell (Media Recovery Disk) and the audio worked fine.

About 3 weeks ago I needed to reload using the same Memory Stick. All is well except the audio. About 70% is clear and about 30% is so muddy that I can not understand it. Most of the 30% is on-line Face Book etc..

Any suggestions?