My addvice whould first be post some hand historys from when u go bust in the HH section of the forum,you whil get a good analysis there.
Also in the golden archive are a lot of good articles on MTT check it out heres one about open pushing at a late stage http://www.cardschat.com/f49/open-sh...cussion-83565/
Try posting some more info so people can give you better addvice.
Your doing the right thing starting tight and then loosening up when the blinds are geting bigger,but what postion are you trying to steal from?
Playing out of postion could be your problem but with out more info its hard say.