If you cant access or remove the hdd, you could install a linux distro on say a usb stick. Then in the linux distro install etcher https://etcher.io/ , download the recalbox image, then install the image to your internal drive using etcher.
NOTE: This will wipe the entire drive (partitions and all) and the pc will only have recalbox installed on your computer. Be aware of the risks and proceed with caution.