Default [Q] Strange Drag and Drop Issue...I need help PLZ!

I loved my xoom running HC and now that I have JB, it's driving me nuts. First it was the loss of flash and therefor all TV sites like abc.com and more importantly Amazon Prime. I did the side load thing and flash si back, but my audio is out of synch with the video and video is often choppy and unwatchable. I can almost live with that except now I can can't even transfer movie files (AVIs and MP4s). I don't think it's a JB issue as this just happened and I've been on JB for a couple of weeks.

Here's what happens. Stock wifi Xoom. I plug in via usb. Computer running Win7 64 bit sees the xoom just fine. I can drag a file from either the internal storage, or the sd card onto my computer. But when I try to drag any file from the computer to the xoom, I get an error message saying "The device is either not connected or is not connected". I've looked everywhere and I haven't found anyone with this problem.

HELP! Any ideas?

EDIT to ADD: Weirder still, I tried a Windows system restore. Now I can drag a jpeg or .doc file, but no movie files, regardless of size or format. CRAZY!