Code taking forever to run and not generating output?

The attached code is that of a mathematical model of a biological system and I'm never getting an output no matter what I'm trying to change. Can someone please tell what's wrong?

[darova]

Try wtih

Tend = 1;

[Rik]

@darova, you are pointing at the actual source of the problem, so feel free to post it as an answer (in which case I would suggest being slightly more verbose).

I also would argue against the use of so may globals, but I'll leave that one to someone else to suggest an edit.