ok, first of all, just go along with what the installer wizard wants you to do. second, the command is chkdsk /f, not checkdisk
the installer should have a guided partitioning option, and just go with that. the recommended should shrink your windows partition and install ubuntu on the other part. do check this step though, if the installer suggests to wipe the disk, and you select it, your data is gone.
but you do need to run chkdsk /f first, as the installer uses the same commands that gparted uses. it will generate an error if your windows volume still has a check tag on it.