Perhaps the connection hardware (cable or card reader) has gone bad?
Please provide more details:
From one day to another LR can't find the (raw) images on my camera... Are you referring to when you import new images, Lightroom doesn't recognize your SD or Flash card? If yes, have you tried other cards? Are you connecting your camera or phone directly to the computer? Are you seeing it on your desktop but not in Lightroom?
Also you mention 'suddenly' in your op but nothing has changed? Do you have auto-update on? What OS are you running?
Cables are ok (different cables for camera & phone). LR finds the hardware but says there's nothing on it.
Yes, when I want to import new files. LR finds the camera but 'sees' nothing on it.
It's LR that gives me the message.
At first, the preview of the files disappeared but importing did nevertheless work.
A few days later, LR says there are no files on the hardware - so importing has
become impossible. With both devices (and different cables).
Windows 8.1. x64
I updated when I noticed the problem but that was no solution.