I'm experiencing similar symptoms. What MC does seems random. When I insert a disk, it lists tracks already ripped from a previous disk. If I click rip, it starts telling me it's ripping the same tracks over again and ignores the inserted disk. Auto-rip works once in 10 times. About a third of the time MC tells me no tracks are selected even though it seemed to be reading the disk. Tracks deleted from Recently Ripped return. Sometimes restarting MC works. Sometimes restarting Windows seems to. Like the first poster, I've tried many things, and now seem to be in the same position of being unable to rip at all.
Ripping has never entirely worked as expected for me, and I've painfully ripped about 100 albums now. My best guess is that something is haywire in the file structure, but I'm beginning not to care. Tagging gives me enough to do without struggling with mechanics.
I very much want the promised results, and I've generally found the Forum to be extremely helpful and quick to respond, but because of this problem, other less serious ones, and documentation which requires too much effort to get anything out of, I'm about to give up.