Computer reboots unexpectedly
I recently purchased a new Dell XPS 8700 (Core i7-4770 processor, 16GB Dual Channel DDR3 SDRAM), added a 2TB Seagate hard disk and installed Ubuntu 13.04 (64 bit) on this new drive. I have even disconnected the original hard disk (includes Windows 8) as currently the PC is only used for Ubuntu. So there is no dual OS. The system is explicitly used to run OpenFOAM v2.1.1, a CFD toolbox. I run OpenFOAM in serial, i.e., one CPU is allocated to each task, and computations may take several days, means some of the CPUs are running %100 for few days (there are total of 8 CPUs). At least one CPU is left unloaded at all times.
The issue that I am running to is that over the past week the PC has rebooted 3-4 times unexpectedly. All the running programs are killed as a result. At first I thought it is installing necessary updates, I checked for all the updated and there was nothing left. I shutdown the system and started again. I even disconnected internet connection, as I did not want any reboot (due to downloading/installing updates) at the middle of OpenFOAM computations. Despite all, the PC rebooted again unexpectedly! The PC is in a room with several other computers (older PCs), and nothing similar is happening to other machines. The computer is connected to a surge protector (not the best one, nor cheapest one), so that may be a reason. But all other computers in the room are also connected to similar surge protectors, and no rebooting is observed in those machines.
I do not find any reason on why rebooting is happening. Does anyone have an idea on what is possibly causing this or how can I stop it? Is there any way (a log file, installing a toolbox etc) that I could learn what forces the system to reboot, or monitor system temperature (this is just a guess)? I appreciate any help very much. Thank you.