Some of these insist on having a certain drive letter being available. The flash drive I have won't be recognised unless F is free. It doesn't want to be F, It can happily be any drive letter. But F must be free. I don't know why, but it solved my problem by switching drive letters about. Have a look on the manufacturers web site, there may be a known issue about this. Also as driving man says, look for a little switch with a lock sign.