You should allow/prompt OS to format the drive but, often a flash drive will declare that it needs formatting when it actually doesn't.
First try rebooting the computer (without flash drive inserted), after OS loads, try it.
If that doesn't work and there is data you would like to keep on the drive, try it in another device that you can copy from, hopefully it will load there - copy the data, put it back in your computer then allow your OS to format the drive
Sometimes a specific brand of flash drive just doesn't work well with a specific brand/model of computer.
Hope it helped