Weird behavior of USB

Hello,
I bought a pack of USBs from EBay auction for a large size but unfortunately it's acting weirdly and none of the USBs is working as the others worked in the past. It is very surprising & shocking for me that the files are copied to USB and process shows that the files are being copied but when I check the USB after finishing the copying process, I see a strange pattern. Some of the files are copied and the folders are there, some folders are there but empty and some are copied with all the information but after a while all the files disappear. I also noticed that all the USBs are showing the same behavior.

It is an abnormal condition for me that I never experienced before in my life and since I am not a computer guy therefore, I wanted to get some help in resolution of this issue from the computer geeks at this forum.

If anybody wants and can help, please help me because someday you may need help too. For your kind information, I am using a laptop with WINDOWS7 ULTIMATE. Although it is a little laptop but it is taking care of my needs for a long time and since 5 years in service many USBs were successfully used on this machine. Therefore I don't think there is something wrong with the machine. Any sort of help will be greatly appreciated.

Thanks.