My DS is like this sometimes, both at naptime and in the middle of the night. Nothing helps him calm down, and anything I say or do, including doing nothing, just makes him scream louder. It is indeed frustrating and makes me feel utterly helpless, so I definitely understand where you're coming from.
Two things I have noticed about it. First, sometimes he seems to wake up but to not be entirely present, as if he's still in a dream state. Although talking to him often makes him more angry, I will periodically ask him questions or say things to him, maybe once every 30 seconds or so. My intent is to get his brain working and help shake him from the state he's stuck in, so I'll talk to him about what he might want to do - go have a cracker or play outside. It usually works pretty well, as eventually he'll quiet down and start listening to my voice and let me hold him.
Second thing I've noticed is that if he goes to sleep with DH or I in bed with him, and then he wakes up alone, he freaks out a lot more than if he wakes up and we are there. Because of being pregnant, I've been taking naps with him almost every day, and since starting that, he nearly always wakes up happy after nap, where before he was at a bare minimum whiny, clingy, and crying for a half hour or so.
Good luck figuring a way to cope. This is a tough one, mama!
Allison.... mom of DS1 (7) and DS2 (4) and awaiting #3 near the end of April 2011