Removable media such as memory sticks are convenient because they are capable of storing a large amount of data in a very small place, but they are also prone to having their data become corrupted without warning. There can be several different causes for the problem that you will need to troubleshoot to repair the memory stick, but ultimately you can reformat the drive and start over if you like.
Power on your computer and wait for the operating system to fully load up. Click the Windows "Start" menu and then choose "Control Panel" from the list of options. Select "Hardware and Sound" and choose "Device Manager" from the Devices and Printers section.
Click the delta to the left of your card reader. Right-click the device and select "Properties." Click the "General" tab. Check to see if the status reads as "This device is working properly" or "This device cannot start."
Click on the "Driver" tab if the status does not say that the device is working properly. Click "Update Driver" and wait for the new driver to download. Restart the computer and attempt to use the memory stick again.
Click "Start" and choose "Computer." Check to see if the memory stick appears in the list of connected drives. Click "Map a Network Drive" if the memory stick does not appear in the options. Click on the drop-down menu and choose a driver letter. Click "Browse" and select the location of the memory stick. Click "OK" and attempt to use the memory stick again.
Right-click on the drive letter corresponding to the memory stick if it does appear as a connected drive. Click "Format" from the context menu.
Choose "NTFS" from the drop-down menu, and click "Start." Wait for the format process to finish. Restart the computer and attempt to use the memory stick again.
Immediately stop saving, opening or deleting files from the memory stick at the first sign of problems, because the way that removable media stores memory can result in permanent loss of data if you keep using it before you fix the problem.