I cant seems to turn on my dynamesh for some reason… i edit it, subdivided it and i did successfully turn on dynamesh before but then i tried to turn it on again but i pressed the button it only flashed orange then back to grey…could it be the problem of my software?
Looks like you might benefit from script file found here http://www.zbrushcentral.com/showthread.php?176896-How-to-clean-the-excess-3D-Meshes-in-the-tool-palette-Answered&p=1011378&viewfull=1#post1011378 
Why haven’t you updated to 4R7?
also, make sure your object is a poly mesh (hit make polymesh) button perhaps.
also, make sure your object is a poly mesh (hit make polymesh) button perhaps.
Gordon, thats a good idea, but looking at this, just the fact that you can see the Dynamesh section of the Geometry Pallet indicates that it is PM3D.
Alac:
Try clearing the mask:
Control Shift A
THEN turn on DynaMesh.
That should do the trick.
You DO NOT need any scripts for this.
If you look at your ScreenShot there is a message where the Progress Bar goes that says; “Note: Mask must be cleared in order to DynaMesh”
thanks for everyone’s suggestion! ill have a try