Dawg

I have a 14.4v DeWalt drill/driver that wasn't used for a couple of years. When I try to use it now, it generally won't turn the first time I press the trigger. If I try to rotate the motor shaft by hand - by grabbing the chuck and trying to twist it - I can get it to move just a fraction of a inch. After that, the drill works. If I stop for a while, I have to do it again. If I switch between the drill's 3 speeds, I generally have to do the same thing again. I have the impression that by trying to rotate the motor shaft, I might be breaking it loose from being stuck and then it works. Sometime just shaking the drill vigorously for a second makes it work again. Any ideas what might be the problem? I'm going to dismantle it and see what's going on in there, but wanted to check a forum first. Thanks.