The steps you describe put the TP into "bootie" mode. That's what we use here to flash an uncooperative device - it isn't the normal USB mass storage mode.
If you have some low-level USB tools (things that let you look at the vendor & product ID of USB connected things) you'll probably see the TP listed there. (I was going to try my test TP, but I've left it unplugged too long so it is just giving me the blinking core-navi LEDs that indicate that it is trying to charge but it doesn't even have enough oomph to show show me the 'white battery of death' screen....)
As for why you can't copy stuff to your TP, I dunno, but edpa.exe is a Symantec(?) data protection app - that is likely interfering.