How can I start a business with a non-compete form from previous employer for 24 months?

First, to state the obvious you can freely start a business that does not compete with your former employer. 
Assuming that's not possible--that you have good reasons to compete with them--then bear in mind that non-competes are enforceable as a general matter. However, courts will, if they are challenged, sometimes reduce the length or durartion of the non-compete, and/or reduce the area/region covered by them that is because courts disfavor or dislike noncompetes, and will only enforce them to the extent necessary to protect the former employer from unfair competition by its former employee while still giving the employee some chance to move ahead with his/her life and provide for him/herself and family.
24 months is a very long non-compete unless you had been the owner or a very senior and well-paid executive of the former company there is a good chance that if you were not, that if you challenged it, you could get its time reduced to between 6 and 12 months, which might help you. It may also be possible to reduce the geographic area, or even the types of work, covered by it.
Non-competes are enforceable as per their language, and the specific facts the nature of the employer and its market your previous level and compensation etc. are critical. There is no way to definitely answer questions about your situation in the abstract. You need to bring the non-compete to an employment law attorney, who can review it and the situation with you in detail and advise you as to options.