So all this worked once upon a time & now 'suddenly' doesn't ? & just to be sure, you can play say '.wav' or '.cda' files from your hardisk - but not from the cd ?
Could well be, this is symptomatic of a few things ..
So what does this page
http://delltech.150m.com/XP/audio/audio.devices.png say
exactly ? ('cos it won't be saying
exactly what you said ;) - or I'd be surprised if it did)
& have you got things like burning software or virtual drive software also ? & does the unit produce sound from the headphone socket on the front of the <a style='text-decoration: none; border-bottom: 3px double;' href="http://www.serverlogic3.com/lm/rtl3.asp?si=22&k=cd%20dvd" onmouseover="window.status='cd/dvd'; return true;" onmouseout="window.status=''; return true;">cd/dvd</a> ?