Most 4350s won't even have a fan, I think pretty much all of them have passive coolers. Overheating GPUs usually won't cause the whole system to lock up though, the video driver would usually crash first or you might get a Bluescreen error. It would help to know which games you are playing that are causing your system to lock up. You may want to check your CPU temperatures. If they are too high, CPU throttling might be causing the system to lock up. You can try CPUID HWMonitor or CoreTemp to check your CPU temperatures. If you don't regularly scan for viruses, you probably should, all sorts of malware infections could cause system lock ups.