Be mindful of what you bring into your model.
Components made by others are often highly detailed standalone models.
They’re nice to look at and perform reasonably well on their own.
But in the context of a larger model their overly complex geometry readily affects performance.
Might you post a link to the computer case model so we can have a look?
This from the SketchUp Hardware and Software Requirements…
SketchUp will run on multiple-processor machines; however, SketchUp will only use one processor. SketchUp doesn’t support hyper-threading or multi-threading at this time.
Modeling technique has a tremendous impact upon performance which no amount of hardware can overcome.
There’s a compendium of performance modeling techniques to be found at the SketchUp Sage.
How do I make SketchUp run faster? — SketchUp Sage Site