Have you tried opening from Bridge?
Have you tried different ways of opening the files in Photoshop? That might help pin down where the problem is.
What operating system are you using? I suspect that is where the issue lies.
I have tried numerous ways of opening the files; right click drag to clipboard, opening from bridge, nothing is working
I am operating on Windows 7.
Graphics card: AMD Radeon HD8490.
And yet PSD and PDF files open OK.... Hmmm... it's a strange one.
Would you mind installing a previous version of Photoshop to test that it is related to CC2018. You can install a previous version along side CC2018, but perhaps CC2015 would be safest.
If it is definitely only happening with CC2018, raise it on the Feedback site where the likes of Jeff Tranberry will respond.
In fact I found this on that site, so there might well be an issue. At least a previous version will get you up and running while it is being sorted out, but you should have to be jumping through hoops like this. We are just users here the same as you, but I still feel the need to say sorry.
So I installed CC 2015 and it will allow me to open files!?!
After installing PS CC 2015 and running some system updates:
Advanced Micro Devices, Inc. - Graphics Adapter WDDM1.1, Graphics Adapter WDDM1.3, Graphics Adapter WDDM2.0 - AMD Radeon HD 8490
Update for Windows 7 for x64-based Systems (KB2592687)
Reopened PS and it is now allowing me to open image files!
Thanks TD for your suggestions.