I dropped my computer and now when I start it up it says:
Reboot and select proper boot device or insert boot media in selected
boot device and press a key.
I thought turning it back off, then on would work, but I get the same thing. I have a Toshiba.
What should I do?
Pretty much what @karel says.
Its possible that the hard drive connector has just been dislodged (hopefully), however it is unfortunately likely that the drop has damaged the hard drive in the computer and will need to be replaced.
Depending on your skill (and to a lesser extent the type of computer) it may be possible for you to open it up and reseat the drive. The exact details on how you do this will depend on the model, but on most computers if you look at the back of them you will find a hard drive symbol (looks like a cylinder) – if you unscrew the screws with that symbol the hard drive will be located underneath, and it may be possible to reseat it.