usb not recongizing Leonardo-windows 7- code 45. can't upload or "see" device

I am having trouble getting my leonardo to stay connected to usb. plug in, tries to start, shows up in device manager briefly then code 45. and disappears. Can't upload programs says board on port... not connected...reset then upload again and still no go. I have had it working up to last friday but all of a sudden the usb driver wont kickstart or something.....please help!! I had IDE 1.5.8 and worked until friday and then started having problems, updated to 1.6.x and still no go!