external usb install

[kalpana]

booted with a rufus usb stick, selected install to what i thought to be my external hd. (not sda or sdb) I've 2 internal hd. Now I cannot boot form external hd and my windows drive D is not accessible (says i need to format to access) Important stuff on D:
that's with the latest lts...
so how to fix all this.
thanks