Hi,
According to your description, please let me know if some error code appear when this issue occurred.
Also, lets temporarily disable Windows firewall and security software to check if that helps.
If it doesnt work, please use manage-bde command to check status of removable drive.
1. Press Win+x, open elevated command prompt
2. Run below command:
manage-bde -status X(removable drive letter)
manage-bde: on X(removable drive letter)
For more information about the command, please refer to:
Manage-bde
http://technet.microsoft.com/en-us/library/ff829849.aspx
If the issue persists, I suggest you check the following GPO setting to check the result.
I would like to share the following article with you:
http://technet.microsoft.com/en-us/library/dd875532(WS.10).aspx#BKMK_gpsettings
http://technet.microsoft.com/en-us/library/ee424316(WS.10).aspx
It seems that these also apply to windows 8.
Regards,