I have an 1993 Ford F250 turbo diesel truck that won't start. I've been told, that the glow plugs are not warming up. Where are the glow plugs and is there anything I can do to warm them up or fix? Do they need replaced? Is it possible that I flooded the truck with diesel fuel?

If your glow plugs are not warming up, then your glow plugs are either bad, or your glow plug relay is bad there is a test that you can do to check them, but it sounds like you've already had that done? It's not expensive to replace glow plugs, so go ahead and do that? Many, many people swear by the fact... Do not use Autolites!!!
they state that they tend to swell, or even break and when you try to remove them, portions of the glow plug remain in the block! Not a good thing!

Are you waiting after turning ignition key on before actually moving key to start position? My diesel I turn key to 1st position;bells and lights;if engine is cold an amber light that looks like a lamp filiment comes on...wait until that light goes out before engaging the starter.