Hello, Sashwat
If possible, test the flash drive in another computer and check if you are able to access it or not. If not, the drive may be bad.
If it is a USB card reader with an SD card, rather than a dedicated flash drive, test if the card is recognized and accessable in other readers/devices. Also check the metal contacts on the card to ensure there is nothing blocking the metal contacts. If the card is unable to be read in other devices and the contacts are clean, the card is likely bad.
If other devices can access the drive, but not through the card reader, the card reader could be bad.
David
Microsoft Answers Support Engineer
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