Oh, the poor little thing. And poor you, too.
My real advice is: find out what's going on. Is it just an adjustment thing, which will pass? Or could he be being bullied (which DOES happen in kindergarten, and plenty of it)?
Sit your son down, give him a big hug, and tell him, "I need to know why you don't want to go to school. If I understand why, then I can help, but I need you to tell me."
Then, once you understand the problem, you have options: You can help him adjust, you can talk to the teacher or school officials, or in a worst-case scenario, you can look for other school options. But until you understand the root of the problem, you don't have the tools to decide.