Main Loading Stuck and Screen Flicker

@KingNoPants  Please try launching the game in windowed mode.  Go into Documents > Electronic Arts > The Sims 3, open options.ini, ctrl-F to search for fullscreen , and set it to 0 (zero).

Another thing you can try is disabling the Parsec app entirely, as in, go through the Task Manager's background tasks list and make sure none of its processes are running, before you play.  I don't know whether it's interfering with Sims 3, but a game this old often doesn't respond well to this kind of software.

If that doesn't help, please test the game on each monitor separately: disconnect the other one and restart your computer, then open Sims 3 and nothing else.  It sounds like you play through Steam, which means you can launch the game directly from TS3W.exe, which is here by default:

Program Files (x86)\Steam\steamapps\common\The Sims 3\Game\Bin

By the way, your E drive is quite low on space.  I wouldn't expect this to cause performance issues with Sims 3 under normal circumstances, even if the game is installed there, but it could definitely be a problem if you've moved the Documents directory to E.  Sims 3 creates temp user files that can be somewhat large.