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I grasp that your USB drives are not functioning correctly. When you tried to format the drive but it could not be found.
Have you checked Device Manager to ensure the USB has not been disabled?
I would try installing the chipset drivers again. Here is a link to the software and driver page for your unit. HP ENVY m4-1015dx Notebook PC Drivers.
If this has not resolved the difficulty, you can do a restore back to a time when they were working. Using Microsoft System Restore (Windows 8)