Sound problems

Hi. I have an older Dell XPS M1710 that I did a windows7 upgrade on about a year ago. Everything has been working fine on this machine up until a few days ago. For some reason I no longer have sound output on any media player program or websites like YouTube. The system sounds are working fine, but when I try using winamp or windows media player or any other application I get an error message saying my audio device is bad or I may have a bad sound driver. I have un-installed & re-installed the correct driver from Dell & have tried everything under the sun to correct this through troubleshooting & google search & have had no luck whatsoever. Has anyone else had this problem? My next step may be to get a usb card, but I'd rather figure it out without doing that. Please help!