A couple of things you can look at
Version of Windows you are running
Can you test it on a laptop
Do you have the most up to date drivers for your graphics card
Have you tried reducing the "Graphics Quality" before clicking play
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Check and see if your antivirus is interfering, try switching it off and see if that helps
Other than these the only thing I can think of is increasing your ram.
Personally these I always recommen 16GB as standard, 8 just doesn't cut it anymore.