Sig. Misquito HELP

[1Longbow]

My brother owns one of the above pistols,we went out shooting today and after racking the slide and loading the chamber ,the gun would not shoot. The trigger pulls to the rear and just kinda clicks. The hammer does not fall nor does the decocker release the hammer. the trigger pulls all the way to the rear,thats when we hear and feel it click. Any ideas as to what is wrong? Thank You [/t][/t]