I suppose your terrain is located to high and you see nothing because when you start, your camera is located buried under the terrain. If that's the case, you would see nothing because the terrain normals are above your camera. Try lowering your terrain in one of the bottom boxes in wed. Next, when you are looking at the terrain in MED, if you click "Model Preview" under the "File" Tab do you see the terrain properly? The guys above refering to the scale is a definate possability. But... if you scale the terrain you should do it in MED not WED. There are a few reasons for this. First, because when you scale a terrain in WED the terrain will most likely be to high as I mentioned and secondly because in A8 a terrain must be scaled in Med and have a scale of 1-to-1 in WED so the Physics will work and you wont fall through the terrain. Actually, what I suggest, is that you visit the Mystymood site and download their Lite-C version of their demo. Then, experiment. You will be able to look at their terrain and code etc... Then you can put your terrain in and then diagnos your terrain problem....
Here is a link to there web site:
http://www.loopix-project.com/Click on "Easy" Then "Templates".... find the Lite-C version and download...
Open the project in wed and start playing....
Have fun and good luck...