If your school does not have a FAFSA code, it means they are not administering any federal aid. To get federal aid, you can't use the FAFSA. You can try applying for any federal grants or loans individually on your own. The federal student aid website will have all the details on how to apply for each grant and/or loans. It is definitely more tedious on your part since your school can't do it for you.
If a school doesn't deal with the FAFSA or have a school code, it is unlikely that you will be able to apply for federal financial aid through the FAFSA. Certain schools don't deal with the FAFSA for various reasons. Check to see if the school you are interested in offers any private grants, loans or scholarships. Also, check for federal scholarships online. There are many scholarships out there for every type of student.
This is a hard question to give a specific answer to. Whether or not you receive a grant from any one foundation or agency depends on a wide variety of factors. Whether or not you qualify for any given grant will really depend on what the grant is being issued for, who the grant is coming from, and what your qualifications for this grant are, and these factors vary widely. There are grants out there that will provide for continuing online education, and many that will provide for disabled students to continue learning. If you do in fact qualify for a disabled student grant, depending on the nature of your specific disability, you may in fact be a likely candidate to receive the benefits of the grant while taking classes online.
If your school does not have a school code, it means they are not administering any federal financial aid. This means, you'll have to apply for each grant and loan individually on the FAFSA website. It does not mean you won't be able to receive federal aid for that school. The FAFSA website offers more information on how to do the process. It is just more tedious for you because you have to apply for yourself instead of the school doing it for you.
You should still be able to apply for federal financial aid such as student loans or similar programs through the FAFSA. Talk to your school's financial aid office or financial advisers for tips on what other students have done in the past. If you run into any problems using the FAFSA it is best to call one of the counselors. You should be able to find the numbers you need on their website or in correspondence sent to you from the FAFSA support teams. You may need to coordinate with your school's financial aid office and have documentation sent to FAFSA verifying your enrollment status.