Unfortunately, it could be almost anything -- motherboard, RAM, PSU, CPU or chipset overheating, or software (e.g. buggy device driver, or even a malware infection).
Does the system seem to run stable otherwise, or have you seen unexplained crashes during other tasks as well?
First I'd run a memory diagnostic like Memtest86. Then make sure you've got the latest BIOS for the motherboard, and the latest chipset, NIC and video drivers installed.
The years just pass like trains. I wave, but they don't slow down.
-- Steven Wilson