works then doesn't

@jackkingsley could be a loose connection on the power button , the power button itself wearing out or even the brushes on the motor wearing down. Time to open it up and to have a look at it. Since iFixit does not yet have a guide for this, use something like this video or the instructions from hereto work on your Dewalt. Once you have it apart you can always take some good picture and post those with your Question. iFixitでの質問に画像を追加する方法 That way we can see what you see and hopefully we can get your driver back to work again.

I just thought of something. How old is your battery. It is easily possible that this is caused by a depleted/failing battery. If this is an older battery I would replace that first.

While you work on your Dewalt driver, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has a device with the same issues as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.

Repair is War on Entropy!