i had no problem with game but i can see "killing floor.exe has stopped working" for 2 days, i dont understand why this error occured i couldnt fix whatever i do

You could try reinstalling it through Steam or the retail version to see if that helps.

not working...

you have to verify the integrity of cache of the game.
go to killing floor , right click it properties , then local files and verify the integrity of cache. Let it do its job and see if that works.
If not update your steam and your drivers