Turning problems, we need suggestions PLZ

[Oumonkey]

Hi, My robot is having turning problems now. Our programming seems to doing what it is to but our robot won't turn. We lifted it up and made sure it was working right and the motors are going in the right direction, but when we put it on the ground the motors will work forward or backwoods but when we try and turn it it just stands still and the motors struggle to move. I think it is the extra traction we put on the wheels to move smother, so if someone can give us ideas to check it would really help us a lot. If you need some more specific details I might not be able to check them for a few days.