Sdhc memory card - usb device not recognized

Hello,
I have a canon EOS and have been using the same SDHC 4GB memory card and reader with no problems. I took several pictures yesterday and when I plugged in my card/reader to my laptop to download the pics, my computer is now saying "usb device not recognized" I bought a new reader and it says the same thing. The same error message comes up in my other laptop too. When I put the memory card in my camera it works fine. I even re-formatted the memory card in my camera and lost all of my pics, but that didn't fix the problem. I tried reinstalling the usb driver and installing the windows 7 updates. I have tried every forum and looked for a fix, but no one seems to have the same problem as me??? Can anyone suggest a fix???