Try "resetting" all your adjustments. Screw barrel adjuster all the way back in on the shifter, along with the barrel adjuster on the derailleur, and unscrew the high and low adjuster screws.

Shift to first gear, but be careful not to let the chain shift past and into the spokes.

Set the high screw limit so the chain won't go past the first gear.

Shift down to 7th and set the low screw limit so the chain won't go past 7th gear.

Try shifting through all the gears. If there are still problems, shift back to 7th, unscrew the cable clamp and pull the cable with just enough force to get the cable moderately stiff.

Tighten the cable clamp and shift through all the gears again. If you still experience problems, use the barrel adjusters to get it just right.

Hope this helps...

Josh