Game Crashing after 5 minutes of gameplay (real time) - screen frozen, clock stopped, sims frozen...

What we are trying to pin down here is how much RAM the game is using relative to its 32-bit limit, not how much is available on or being used by the system in total. The OP is experiencing 100% CPU usage at the game's startup, this is not normal either, and we should like to find out what's causing that if we can where it wasn't happening before.

Yes, certainly lack of RAM to work with will cause all kinds of unwanted issues too. But with 16 GB total and the player not reporting a shortage of RAM overall, I would say this isn't necessarily the first place to look for trouble.