dont understand what you mean by:

'but i can only swith between preset, not activate it.'

I assume you have patched a DMX 'preset trigger' single channel in the catalyst control window?
The DMX value of that channel will then recall a specific preset relating to the DMX value (note - there is an offset to allow for manual desks that dont go all the way to zero)

Do you have the same layers (or mixes) patched to DMX control?

Presets will only work on those layers (and mixes) if not controlled by DMX.

To clarify - you can use DMX to set up a look and then snapshot in to a preset - but to recall that preset - you would have to turn off DMX control for that layer

Hope this helps

Simon