suddenly can not load RAW photos into lightroom 5. Never had trouble in past. Can still load Jpegs. Recently upgraded operating system to Sierra.
Did you change to a new camera?
Please check at this link which version of LR you need to support your camera: Cameras supported by Camera Raw
Free upgrades to the latest LR5 can be found here: Download Photoshop Lightroom
If you need a LR6 version, this will be a paid upgrade or you can use the free DNG converter to convert to DNG and then import these into LR5 if you do not want to buy an upgrade.
I have Panasonic GF7 which I see that you need Lightroom 6 or higher.
You'll have to upgrade or use the free DNG converter. Your choice.