What are your idle and load CPU temps? The specs on your RAM are pretty poor. Have you performed an overnight Memtest86+ test to check for faulty RAM? Freezing problems are usually caused by either faulty RAM/incorrect RAM settings in the BIOS or overheating.
Have you run Memtest86+ on the new RAM kit? I haven't been impressed with OCZ RAM lately. It wouldn't surprise me if the new RAM is also faulty. You should also manually set the RAM speed, timings, and voltage to their rated values in the BIOS.