Make sure you have done the following...
- Install Warcraft III: Reign of Chaos.
- Install Warcraft III: The Frozen Throne.
- Installed Patch 1.26.0.6401 (latest at time of post), anything lower is not supported so we cannot help.
Make sure the install path is reasonable. A reasonable install path should look like...
If the install path is too long (either too many folders, or too long folder names) WC3 might break and be unable to see maps and make certain files.
When trying to play custom maps such as downloaded from the
Maps section make sure to place the map somewhere in the
"...\Warcraft III\Maps" folder. The usual place is the
"...\Warcraft III\Maps\Download" folder as that is where maps for multiplayer games are downloaded to. If the map file name is very long consider shortening it. If the folder path of the map is too long or the map file name is too long then WC3 will not see it.
If you mean that the map is not appearing in Explorer after saving then that is like the result of incorrectly set permissions. Try running the map as administrator and when saving save into a folder which as administrator you have given full control to all users.