OK. Which Reader do you have?
I have the 505 and have only had this happen once. I waited for hours with that little circle on the screen and gave up and tried the Soft Reset (twice)... of course this was after the panic and push all the buttons technique that a lot of us seem to do.
I used a paper clip to push the reset button on the back of my 505 and then slid the power switch. I waited a little bit and then did the same again. The little circle starting turning again and finally opened.
You can click on the link in my signature for the link to the MR Wiki with the Sony Troubleshooting Guide for the Soft and Hard Reset instructions.
What file formats have you been putting on your Reader?