I suppose you have tried clicking on the "Flatten" icon and it didn't work. Am I correct or do you need help in finding it (the command)? If you have tried to flatten and it won't, we will need a bit more information. Can you attach your file?
According to the sheet metal training book I have, you need to use the "insert bends" command on the cylinder I have attached. This file is the training file from solid works sheet metal course 2010. (see pdf attached)
I suppose you have tried clicking on the "Flatten" icon and it didn't work. Am I correct or do you need help in finding it (the command)? If you have tried to flatten and it won't, we will need a bit more information. Can you attach your file?