|"I had not used any anti-malware programs until now..."|
You stated in your first post...
"After a virus attack which I resolved,..."
If you had not used any anti-malware programs until now, what did you do to supposedly resolve the problem ?
Do you know the name of whatever the malware was or can you describe the symptoms ?
No one anti-malware program finds all malware these days. You may need to run several of them in some cases to find the malware. There are many free online scans that can be done without having to install any more than a minimal amount of software on your computer. If you run a FULL scan with whatever anti-malware prgram you DO have installed, it often finds malware it's resident module that runs all the time doesn't find.
When you plug in a flash drive, a window is supposed to pop up on which you are supposed to select what you want to do or which program to use to examine it - are you seeing that ? If yes, are you closing that window BEFORE you attempt to eject the drive or use the Safely Remove Hardware feature to STOP accessing the drive ?
Also, when you plug in a flash drive while Windows is running, you should see a window pop up that says it is scanning the drive (to find out what types of files are on it) BEFORE you see the above window pop up Are you seeing that ? If yes, are you closing that window if it's still there BEFORE you attemprtto eject the drive or use the Safely Remove Hardware feature to STOP accessing the drive ? (That window disappears once the drive's partitions has/have been fully scanned).
"In Safe Mode, I plugged drive then tried to eject, but same problem."
OK, good to be informed about.
That indicates your problem is not caused by some software that loads when you load Windows normally that is not loaded when you load Safe mode.
"If I restart Windows with flash drive plugged, always goes to 'select' Safe mode but whatever I select it returns to this screen. If I unplug the flash drive, Windows starts up as normal."
You didn't mention that specifically previously.
That probably indicates it's a software problem, not a hardware problem, since the flash drive is recognized fine when you plug it in while Windows is running.
Try loading a previous System Restore restore point with a time and date just before you first had this problem.