Did you try using VdmSound (
http://vogons.zetafleet.com/ndldownload.php?filename=VDMSound2.1.0.exe) before running DOTT? Some of the old games don't work in newer windows environments, but VDMS emulates the sound characteristics of old-school DOS. Be sure after installing vdms, when you run the DOTT.exe file, right click and choose the vdms run option.
If this doesn't work, you can try using ScummVM (
http://www.scummvm.org/) with DOTT.