The following information is taken directly from finaid.org. There are only excerpts here. Click the link to get more information on Financial Aid and what to do if your parents can't or won't pay or fill out the FAFSA.
The federal government and the schools consider it primarily the family's responsibility to pay for school. They provide financial assistance only when the family is unable to pay. If a family just doesn't want to pay, that won't make a difference. Parents have a greater responsibility toward their children than the government or the schools.
The US Department of Education has published guidance to financial aid administrators indicating that neither parent refusal to contribute to the student's education nor parent unwillingness to provide information on the student aid application or for verification is sufficient grounds for a dependency status override. This is true even if the parents do not claim the student as a dependent for income tax purposes or the student demonstrates total self-sufficiency.
Remind your parents that submitting the forms does not obligate them to provide support, but that if they refuse to file the FAFSA, you will not be eligible for any need-based aid on your own.
College financial aid administrators are permitted to offer dependent students an unsubsidized Stafford loan without requiring the parents to file a FAFSA, provided that the financial aid administrator verifies that the parents have ended financial support and will not file the FAFSA. The unsubsidized Stafford loan is not based on financial need and is a loan, but at least it's something to help you pay for school.
But if you can convince your parents to file the FAFSA, you might qualify for need-based aid, such as the subsidized Stafford loan, Perkins loan, and Pell Grant, as well as institutional aid. By not filing the FAFSA, they prevent you from getting any of this aid. (More information at the above bolded link.)
Click on this link to see information on: What to do if a step-parent refused to give information for your FASFA, if parents don't want to take out loans or pay for education, if there is messy divorce, and unsubsidized Stafford loans without parental information.