Make sure your at this building.
When you walk in it should look like this:
In Pokémon HeartGold and SoulSilver, the GTS has the same interior as the one in Platinum.
The Global Terminal in Jubilife City in Pokémon Platinum
The Geonet also reappears, on which players can indicate their location, and on which small dots representing players they have traded with will appear.
The ground floor is the room seen when entering the Global Terminal. It can be reached when in the other floors by using the blue warp panels. There are four points of interest on this floor; the Global Trade Station which is located on the north-western corner, the Geonet located just below it, the Trainer Rankings located on the eastern side and the northern set of blue machines, and the Battle Video Rankings located just below the Trainer Rankings, in the south-eastern corner. The information desk is located next to entrance, which contains two ladies that will give information about the Global Terminal. There are also the warp panels
Basically make sure you are going on the right Warp Panel. I beleive that is your problem.
Hope this Helps ^^