In VegasPro 14, the Set In Point and Set Out Point in the trimmer can only be set when the video is played, not when de video is paused. This is different than in earlier Vegas versions and very inaccurate.
Open a videoevent in the trimmer, position the cursor somewhere on the timeline in the trimmer, press I or click Set In Point button, set cursor to another position on the timeline and press O or click Set Out Point button. Nothing happens, there is no region selected. Only when you play the video you're able to place In and Out points, which is different to earlier Vegas versions.
This is strange behavior. I've looked for some setting that will duplicate the OP's problem -- but can't find anything. Hard to believe this would be a system problem.
I think it may be related to the new feature "Enable Hover Scrub". That allows you to scrub through the Trimmer clip by moving the mouse in the video section of the trimmer. When playing the video in the trimmer, those vertical scrub lines disappear and that might be why you can set the in and out points. Try right clicking in the Trimmer window and de-selecting that "Enable Hover Scrub" option to see if it helps you. I had a hard time finding that option to turn it on again, so if that happens, hold down the Shift key when you choose Preferences from the Option menu. In the Internal tab search for Trimmer and you should see the setting there.
Unfortunately, this doesn't solve my problem. I'm still not able to place IN and OUT points in the Trimmer timeline, either with the keyboard commands I and O and either with the the appropriate buttons in the trimmer window. On the same PC, with also Movie Studio 13 and VegasPro13 installed, this works fine...aaahhhaa,...in VegasPro14, I have in the Preferences/Editing the Option "Collapse loop region when no time selection is present" selected, deselecting this option SOLVES the problem....🤓
That's it, "Collapse loop region when no time selection is present" .. That does it.
I've never applied this setting as the loop regions don't bother me. But it should have nothing to do with setting an in and out point in the trimmer. You wouldn't expect that. I checked VP13 and VP12 and this setting has the same result in those versions. I'd say it is a bug that should be fixed.