Most Likely a Shader/GPU underpower issue, With your Graphics Tier, you should NOT be running on Unlimited, High or Medium.
A 4300/4500 Series Chip has 80 Unified Shaders and is 2+ Generations Old, That is not enough power to Run on Unlimited or High and maybe even Medium, Regardless of resolution, More importantly if they are mobile or integrated GPUs instead of Discrete Versions, there is no active cooling fans on them So they'll overheat within minutes of running GFX intensive games, causing issues.
In comparison A 5830 has 1120 Shaders, 5770 has 800, 5750 has 720..
The Discrete 4300/4500 GPUs Stats are:
the 4350 has 600Mhz Clock, 80 Shaders, 64 Bit memory interface. 800 Mhz Memory
the 4550 has 600Mhz Clock, 80 shaders, 64 bit memory interface. 1600 Mhz Memory
Integrated/Mobile Versions are clocked slower and share system memory.
the 4300/4500 Series is Meant to be for Integrated, Mobile or Low Power/Low Profile Hardware Acceleration for Video, Not for gaming.