I attend online college and had to buy a computer in order to attend. Why is it not showing up as a deduction?

Don't enter it in the box TurboTax gives you to enter computer, software and internet service.  Instead include it in the box Books and materials not required to be purchased from the school.

To be eligible for the tuition credits, the course must be taken at "an eligible institution". The school should be able to tell you if it is an eligible educational institution. In general, an eligible educational institution is an accredited college, university, vocational school, or other postsecondary educational institution, including accredited, public, nonprofit, and proprietary (privately-owned, profit-making) postsecondary institutions. Additionally, in order to be an eligible educational institution, the school must be eligible to participate in a student aid program administered by the Department of Education. If they issue a 1098-T they are probably an eligible institution.

Enter your school at the link below, to see if it's on the dept. of education list.

https://ope.ed.gov/dapip/#/home

Rule of thumb: if you have to ask, your school is not an eligible institution.

Schools that only offer online courses usually do not qualify.  Online classes taken at schools that also have  classroom instruction usually do count.