Whirlpool dryer doesn't finish cycle?

I've looked at whirlpool related questions but haven't found someone with a similar problem.

At first, the dryer could dry the clothes with no problem except it needed about four hour break in order for it to work again after it finished. If I pressed the start button in between that four hour break period, it would makes the noise it does prior to starting except it didn't start.

Recently the dryer has gotten worse and dries clothes for about 20-30 minutes instead of the 60 minutes it originially did. It still takes another 4 hours before it works again for just about 20-30min.

By the way, I usually dry clothes under the automatic regular setting. I've noticed that the little stick that indicates where the dryer is at in the cycle doesn't move when the dryer works for that 20-30 minutes.

Any suggestions on the solution to this would be appreciated. Thanks.