SAFE TO REMOVE

I've got a built in media card reader in my home computer. When I'm through
reading my SD card I've taken out of my camera, I choose to "safely remove"
this from my computer, as I've been led to believe, so I won't loose any
data. Problem is, that when I do so, the drive(s) (actually there are four)
dissappear from my Windows Explorer and I cannot use them again. Recognized
in system/device manager as USB controller/ mass storage device (with the
exclamation mark attached) and properties suggests tha I unplug it and plug
it back in. Impractical as it's all internal.
QUESTION: How can I reactivate this drive? Do I really need to "safely
remove" it each time?