Default Deleted ROM

A friend of mine accidentally deleted his ROM on his LS980. I took his phone home today to try and fix it for him.

It still boots into TWRP (luckily). I tried ADB sideload, and I manage to install ROMs with no issue, but the device boots right back into TWRP on its own. I also have access to download mode and tried the LG FlashTool but it doesn't do anything. I've followed the instructions for it and I just get the COM41 port saying "READY!!" and stays there.

Any advice would be greatly appreciated, he's been out of a phone for two weeks now.

Edit: This is the error on TWRP. "E:Unknown File System: 'datamedia'"

Edit: Fixed. I didn't set the phone to COM41 in device manager. Oops.