This has just started happening the last few months and it's quite annoying. I can use Alt+G to go to the class definition and also function cpp definitions, but my hotkey for h/cpp does nothing. It's quite intermittent but continues to work on some files but stops on others. Seems also that it works everywhere when i first open a solution, but then gradually degrades.
What happens if you press the toolbar button for Alt-o? Are all of the files listed in the OFIW dialog? Are they still listed if you close them, so they are not showing in the IDE?
The obvious reason for this is that VA cannot find the matching file.
If OFIW, if you filter it on the problem file name, without the extension, how many files are listed? Just two? More than two? I am wondering if VA is seeing a group of files, and somehow getting confused.
To be honest no. Process explorer will help you check which processes are running, but that's not the same.
From experience most programs do not install a global keyboard hook. Media players and screen shot tools are the main programs that I have seen do this.