AW: It may happen that the file system of your USB memory device is damaged: by high frequent write/re-write cycles, inappropriate usage (including storage), errors on first format or some other reasons.

Windows OS for example offers 2 different ways of format, quick-format and full-format. In such problem cases it is advisable to perform a full-format with FAT32 as file system.

Note: if even after full format, your USB devices are still not detected, it may well result from an incompatibility of the data carrier controller-IC. Please try a different brand/maker.