Sometimes Windows gets mixed up with these drives and no longer recognises them, you might resolve it by going in to disk management and assigning the drive a new letter.
The other issue where it wants to format the drive can be caused by not 'ejecting' before pulling it out.
We all do it and usually get away with it especially since about Windows 7, but if it's doing some kind of indexing at that moment it might cause problems next time.
This might not help with your present problems but worth bearing in mind. 
Sometimes just plugging in a different port if available will have a more favourable response, or try a different PC if possible.
A worrying number of flash memory cards are actually fake and Sandisk is the most widely faked.
Even what you'd think a reputable seller e.g. Amazon will sometimes get a dodgy batch.