Tasks which are 'demanding' usually means that the CPU is running at 100% for a long period of time. A freeze in this case usually means that the CPU is overheating. Check that the CPU fan is spinning, and vacuum excess dust from your CPU fan and case fan(s). Make sure there are no obstructions (like IDE ribbon cables) blocking airflow.
These tasks are also memory intensive. You can check your memory with
memtest86.