IPhone message "...Insert a valid SIM with no PIN lock to activate iPhone"

I am currently using the iphone 3gs but I have an iphone 1st gen that I was using as an ipod. It was working perfectly fine until my brother put his sim card in it which is from a t mobile phone to see what would happen. As soon as he did that my phone went to the cd-rom and usb screen. All it says is "No SIM card installed, insert a valid SIM with no PIN lock to activate iPhone" altho I already put my sim back in it. Im able to see my pic when I slide it to the emergency call screen but everytime I connect to my comp it say to "disconnect and rettach your iphone now..." I have done that a hundred times. Im out of ideas.

HELPPPPP MEEE!!!! PLEASE!!!!