Looking for career advice

So I mentioned a few weeks ago there was a chance I would be laid off. Well, thankfully I still have a job, but I have a problem as well, and I wanted to know if any of my fans/readers had any legal background, especially for employment matters....

I've had my job for quite a long time, and I like it, I enjoy it, and I believe I do a good job, I get all my tasks done, etc... - For the past several years, I have not gotten any kind of formal job feedback or review; no yearly performance review, nothing... I still got the typical raises everyone got, so I assumed that, since my boss wasn't giving me feedback, I must be doing OK.

Now I have a NEW boss, and he has said my performance is sub-standard and he has demoted me. He gave me a few reasons why he made this decision, but I don't agree with them, and even if I did, none of them are impossible to fix with a little guidance and mentoring (something I've never actually gotten here, sadly).

This is really stressing me out, and I feel like it could have a longer term impact on my career path if this demotion goes on my resume, etc... So what are the rules for this? I don't work for some mom and pop company, this is a large, publicly traded company, so I feel like this is violating my rights as a worker somehow, but I don't know enough about this stuff to really dig into it. Can anyone out there help? Is there some sort of rule about this I can look into?

And no, this has nothing to to with my wheelchair, I'm very certain about that.