nob is keep turning what to do ?

You may find if it's a push fit knob on a half flat shaft then the collar in the knob may be split but tight enough to select a wash/dry but can be turned onward without turning the shaft which would be apparent if the cycle changed.
Of course these are timers and can only be turned one way I hope you haven't tried turning it both ways!
find out from you local store about getting a new control knob. and ask if it's a push fit type.

Bob
October 2005