My MP4 Player Became Unrecognizible. Why?

Hello,

Today I plugged my MP4 player into the USB port of my DVD player in my car (Eonon E1012), but it did not want to read it. It opened a file reading menu on the screen of the DVD player, but it couldn't show any entries. After a while, the MP4 player as well as the DVD player seemed to have frozen up. I unplugged the MP4 player from the DVD but the screen of the MP4 remained as if it was plugged to the USB port. It became non-responsive, even when I tried to switch it off from the power button. I had no idea what to do so I pressed the "reset" button I saw on it. Well, that turned it off and I was able to turn it back on through the power button. However, after I plugged it into my lap-top, I got a message that the device I have plugged in has malfunctioned and the compter does not recognize it. It seems as if the MP4 player is working properly, other than the computer cannot recognize it. I tried my wife's lap-top and got the same message there. Just as an additional information, this exact thing happened with an SD card I used a month ago. I am not sure if that could have caused the problem, but after I checked the compatibility of the DVD player in my car, it turned out that it can read SD cards with maximum of 2GB. Well, the SD card I plugged into it was 4GB and the MP4 player is 16GB. However, the stored data on each one of them is 1.6GB. What can I do to make my lap-top start recognizing them again so I can add or remove data and use the additional storage on them? Thanks a lot for your help!