Having seen the tank set up in your other threads etc, i would vote there was either something under it (grain of sand, etc), or nothing to support it. I would vote the first.
From the pic in your other thread, it seems your tank has an integral support, the big plastic band running around the bottom, which covers the bottom and supports all four corners. You dont need to put polystyrene under these tanks. Which only leads me to think there was something between the glass and the unit it was placed on, which from what i can see, isnt an aquarium stand.
Its not too much of a problem with small tanks (80 odd litres or less) but when you start progressing up the sizes of tanks, they need proper support to stop the above happening.
I would bin the tank and buy another second hand one if you or someone close cant effect a proper repair to the tank.