Like dan said. go slow and check everything. make sure you aren't off a click. If your shifters are actually on the middle click when the chain is on the big chainring, one click will drop it all the way to the der stop. real easy mistake to make on the fd. try releasing the cable. check everything. clean and lube the brifter. (essentially wash it out with wd40), then re-connect the fd and adjust. sometimes doing it again, you will undo a minor error.