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The first basic check you can try is removing your pen drive by using the safely remove icon on the taskbar. Click on safely remove hardware, select your drive and then click ok. Plug the drive back in again and see if this time you can access it. You could also try, plugging your pen drive on another usb port. It might be that your port is not working properly.

One of the reasons a pen drive is sometimes not recognized/open is not having a drive letter assigned to it. To check if that is your case, open My computer and see if your pen drive is showing and also if it is showing a letter for the drive. If it does not show or it shows but you can not access it you might want to try the following:

– click Start
– click Run
– type compmgmt.msc
– click ok
– click on disk management
– check if your drive shows there and highlight it
– right click on your drive
– select the change drive letter and paths option
– assign a new drive letter. Make sure the drive letter you choose is not being used
– click on ok

You also might want to check your device manager, under the usb heading if your pen drive shows there and if it shows, does it have any kind of exclamation mark or shows problems with it.

Another reason for a portable drive not to show, is due to malware/virus. Make sure you run full scans on your drive/computer with your antivirus of choice and also with Superantiware/Malwarebytes. If after doing this, it shows clean then you could probably have a problem with your registry.

Sometimes by editing the filter on the registry this problem can be fixed. As a warning, playing with the registry is a tricky procedure that can ruined your computer completely. If you are not comfortable, ask somebody trained that has more experience with dealing with the registry. The first step when trying to make changes on the registry is to back it back. Here is a link explaining the three possible ways of backing the registry:
http://windowsxp.mvps.org/registry.htm

Ok, the following is the registry fix:
– click on start
– click on Run
– type regedit and click on ok
– once registry open locate the Upperfilters registry value on the following path:

HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlClass{4D36E980- E325-11CE-BFC1-08002BE10318}

– right click on the entry and select delete
– click on ok

– following the same steps as before, find the LowerFilters registry value on the following path:

HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlClass{4D36E967-E325-11CE-BFC1-08002BE10318}

– right click on the entry and select delete
– click on ok
– once both entries are deleted, close the registry editor and then
– restart your computer
– once computer finishes starting up, try your pen drive again, and hopefully this time, it will work. Hope it helps,