How come my front windshield wipers wont work

The windshield wipers will not work. I can here the motor and it sounds like it is moving at the correct speed for the speed I put them on, but the wipers themselves do not move. Any suggestions on what might be the problem, and could I fix this problem myself easily at home?

Thanks!

When I got the van sometimes when you hit the turn signal for a right turn the wipers would come on.
But now they will only work in the lower intermediate range, but just barely. The washer part works just fine, hit the washer and they come on. The rear one works fine.

We checked the fuse and the relay( we did change the relays) and they seem to be fine. My mechanic replaced the switch on the column, but that was not the problem, so he replaced the wiper module, still the same problem. So we are stuck without wipers. What else could cause the wipers to not work. Also is there a plug in where if I took it to say advance auto for them plug it into a diagonostic.