Either 2 or 4 screws hold down the top to the front. Remove them and you can raise the top on most models. From there you can get to the screws that hold the front on. Once you get the front off you can access the gas valve assembly. Before attempting any repairs it is a good idea to clean up the dryer. Get all the lint out and clear the vents. Most of the time you are going to have a blow fuse. This keeps the gas assembly from working and setting the dryer on fire. If all the fuses are good the the flame sensor may be open if it has no continuity then that is the problem. If your sensor is good then most likely you have a bad igniter. If your igniter is ok then them operator coils are probably bad. They will half way work and quit if they are going bad. They get real hot to the touch also if they are going bad..