Microns are really fantastic pens so don't give up hope on them just yet. As others have said, lay them down on their sides or tips down for a few days and see if they revive themselves. The ink surely hasn't dried up if they haven't been opened. It's probably just the felt tip that has dried.
If they don't work after a week or so, I'd still hang on to them. The tips on a Micron can actually be interchanged. So if you have a working pen that dies, you can take the tip off (google a how to..) and salvage the ink in any that don't work.
(I am very rough on the smaller size pens and often damage the tip before I use all of the ink. So I almost always have to switch the tip with a larger size to use it all. I hate wasting good ink!)