Cant read codes ? Any ideas

[redrat]

My check engine light came on so i went to the local Parts store ( Oreillys, auto-zone, advanced ) and the OBD2 scaners kept saying it wasnt conected. i treid 3 diferent scaners and they all say its not conecting. All the pins on the OBD2 plug are strait and the wires are still conected at the back side. I have checked and cleared codes befor but now it wont conect to the computer.. its on a 2003 GMC. Any ideas on what to do to get it to conect?? And yes i had the key on

Thanks for any help. Ryan