We'll need more information than you've given - such as which Cakewalk program you are using? What OS? What drivers are you using?
I suspect this is a sound card conflict. Does your system have another sound card beside the Delta? It is likely that the other card is only 16 bit capable. You will need to disable it in Sonar.
You may also have a driver conflict - MME vs WDM, and that is why the Delta is not showing.
If you do have another sound card, and are not using it for anything, you might want to disable it in Windows and/or the BIOS.