I assigned a shadow to some of my models and now my game is laggy what can i do to make the game playable again except from deleting some shadows

Check out shadow_stencil in the manual; you can use several types of shadows for your models - some are rendered faster.

or you can try use CAST, it less your shadow, but can win some FPS

tnx for the help

What you can do for shadows for static models used as props i.e. a tree or lamp post-- is remove collision detection (frame rate boost for some objects), create simplified brush based geometry marked as detail over the prop, mark invisible, and build. You will get light mapped shadows, simplified collision detection which add up to visual goodness and fps boost (possibly).