[mp7 not firing when i pull the trigger...]

i have what i think is the new wave rice (we) mp7 ,

my problem is when i pull the trigger the hammer sounds like it is going forward but it wont fire,

i am new to this gun bought second hand the previous owner told me that it would need a new plastic

part so it can fire but wasn't sure so any help would be great i know its not much to go on but its all i have cheers .....