I didn't think you could make an SKS not work!
I'm sure it's something small. I have seen people fight with a Yugo for an hour to get it to work. When they asked for our help, we flipped the gas valve open for them. I have also seen people grease the op rod and that caused malfunctions. These should be run dry (in case you didn't know.)
Did you strip it completely? Here's a link.
http://www.surplusrifle.com/sks/carbine/index.asp