My coffee grinder's strange condition. What's wrong?

I've had a black Krups F203 coffee grinder for a long time. I should also say that I have the same grinder in white that I originally bought for grinding spices. I could start using the white one in its place but I really would love to keep using my original black Krups coffee grinder. Here's the problem: my black Krups coffee grinder stopped working recently but it's really strange. If I turn the grinder upside down on my countertop--without any beans, of course--and press the bottom of the grinder against the countertop, the grinder works perfectly. When I turn the grinder right side up, the grinder stops. It happens every time. Upside down, it works. Turning it around to the normal position, it stops. I would hate to toss it. What could be causing this strange condition?