Microsoft back-up function crashes PC

I have an external floppy drive that I use for back-up. As long as only 1 disc is required all is OK. However, when I require more than 1 disc(for Wordperfect files) & get the message to insert the next one, when I press the button on the drive to extract the disc, the PC crashes & automatically shuts down. I run scandisc & it tells me I have 65,536 bites in 2 lost file fragments. I discard them, run backup again & the same problem. I have tried uninstalling/installing the backup program but itdoesn’t help. To complicate matters, it does work sometimes but mostly not.
Can anyone shed some light on what the problem might be & how to correct it?
It’s probably obvious I am not a techie, so please be gentle!!
Thanks, Nick.