How do I cope as a parent of a disabled child?

Talk to others. Coping with a disabled (or "differently-abled") child can be difficult if you do it alone. Gather as much information as possible about the disability. Seek assistance through support groups from your local hospital or doctor's office, national organizations or the internet (research the credibility of the website.) talk with friends, counselors, your physician, and clergy for support.
Get support. For almost all types of disability there are support groups for parents. These can be enormously helpful because you will meet people who have struggled with precisely the issue you are struggling with. They seldom have magic cures but they do provide collective wisdom. This is real hard stuff and the more resources you have the better. Look to organization about the specific disability.