flash drive not recognised

I have a 64 and an 8 gb USB I was using my 64 on my android box then replaced it I formated it I have also done the same with the 8 gb after which they are not recognised when I put them int the computer nothing shows up on the removable disc for either of them can you tell me how to remedy this or as far as  I am led to believe sandisc is guaranteed for life and if so how do I get a replacment as the two these are usless and cant be used please advise.

Kind regards don

This is the link for returning the drives:


In the future when you are done using a drive simply delete the files and folder on it.  Formatting is not necessary to start over.

Thanks for the information 

Kind regards don