I have a 1098T but no able to claim the amount on TT - why not?

What do you have in box 1 and box 5 of your 1098-T? I think your box 5 scholarships must be greater than box 1 tuition. The IRS has a great brochure that explains how scholarships and tax credits interact to help get you a credit.

Alternately, if you are being claimed by your parents, they get the college credit, not you.

Are you the student or the parent? Most students aren't eligible for a tuition credit.

There's a new urban myth among college students that says they can get a $1000 from the government just for filing a tax form. For most of them, they simply aren't eligible. A full time unmarried student, under age 24, even if you don't qualify as a dependent, is only eligible for the refundable portion of the American Opportunity Credit if he supports himself by working. You cannot be supporting yourself on parental support, 529 plans or student loans & grants. It is usually best if the parent claims that credit. 

You cannot claim a credit if you are, or can be, claimed as a dependent by someone else.

Reference: Line 7 instructions for form 8863. https://www.irs.gov/instructions/i8863