S3 and windows 7

We cant get an s3 (galaxy samsung running android) to be recognised by windows 7 laptop. The exact same port and cable works fine with an S4 which is read  by the laptop, and files can be copied off etc. can anyone suggest any tips... windows reports drivers are current. tried to rebooting, taking SIM out etc etc. Some google searches show it is very common but the solutions did not work.