After - Turn on USB storage.... External Card is not accessible When I turn on USB. Internal memory is accessible but having issues with external card.

Even after turn off. No app is working, installed on External memory.

Rebooting device will make everything normal again.

Please Help.
The problem is happening that when you connect your phone to your computer via USB it attaches (mounts) the card to your computer and while that is happening the card is not accessible for android system. This breaks all the applications which are moved to SD card.

This might be device specific to change (if possible at all), so please post your device info.