Jeff,
Let's take PM completely out of the equation then. Go to your files in Windows Explorer and select several RAW files and use the 'Open with' command that appears when you right-click on the selected photos and choose to open them with Photoshop. Do they open all at once, or one at a time?
If they open one at a time, then I think there is something wrong with your installation of Photoshop and you should contact Adobe for help. If they open all at once, please let me know.
-Kirk