What type of sound card do you have?  If I remember correctly, direct x tries to either replace the existing driver with one that has direct x code or puts a wrapper around the existing driver.  It could be that it doesn't support the card.  Does the sound card work otherwise?

My dimension is one of those "slim/skinny" types which has the sound integrated into the motherboard. My computer was working fine up until one month ago. Ever since then, I would get the error code 0x88780078 everytime I try to play music. The only sounds that will work are system sounds. If I open Sounds and Audio Devices Properties, the volume tab will show No Audio Device (and hence, no volume control).