Extra drives on startup

We have HP a1247c computers at work and every time they start up they find additional external hard drives that don't exist. They'll disappear if we select "remove hardware" and "stop" them.

It's not too big of a deal... more of an annoyance... except on one computer the previous owner reformatted and made the main drive I: not C:. Now on startup there's errors that pop up because it can't find certain files in the C: drive etc etc.

I know the simple solution to that is reformat it again and we're in the process of doing so but there's a bunch of important files in there so we want to make sure none are missed and it'll take a while.

And again... it's annoying to see a bunch of extra external drives.

Anyone know why it happens and how to stop it?

Yes there are card readers. Is there any way to make the computer only recognize them if there's media in them?

On my laptop I have sd/smart card/express card readers but it doesn't create those extra drives.