Try different learning methods. Kids learn differently. Some kids learn by hearing things, some by visualizing things, and some by touching and doing. It's not a disability - it's what makes the world full of artists, sculptors, composers and musicians, computer experts, teachers, physicians, scientists,chefs, plumbers,police officers and fire fighters, designers, carpenters, gardeners, auto mechanics and astro-neuro-geo-physio-thermo-nauts (yeah, I made that one up).
Buy very rough sandpaper, and cut the letters out of it (use a stencil or just draw on the back with pencil). Make the letters large and thick. Then have him trace the rough sandpaper letters with his finger. Make a game out of having him close his eyes and feel the sandpaper letter and then guess what letter he traced with his fingers.
Draw letters in shaving cream. Shape them out of Play-Doh. Paste large letters (you can buy them at craft stores or cut your own out of construction paper) on things in your house, like a D on the door, R on the refrigerator, W on the window, his initial on the door to his room.
Make up little rhymes or chants. While you're tracing the letter F say, in a sing-song, hip-hop way, "F is for fire and F is for floor. F is for fly and F is for four." Or something like that. Or look up kids' alphabet songs and videos and just play a CD of alphabet songs while you're making cookies (which, by the way, you can shape into letters! Same with pancakes!)
But most importantly, relax. Kindergarten is not the be-all and end-all of literacy. He's learning so many other things - socialization, how to sit quietly and listen, how to hold a pencil, how to listen to a teacher, how to cooperate with other kids, etc.
And make learning fun. Make it a part of your day, not a tutoring session or a "you've got to get this!" kind of thing.