Gear Problems on Shimano 105

craigsneilson Posts: 11
edited September 2008 in Road beginners
I've just had to change my back inner tube, but I've put my rear wheel back on and I can't change gear on my front hub. I'm using got Shimano 105 gear set - the bike has recently been serviced, and they completely wasted my time, so I don't really want to take it back if I can fix it myself

Any ideas, I can't change down to the smaller cog.