OS restart when using Regnum

[Anpu]

Hi, I have a following problem: I log into Regnum and after like 5 minutes, my system just resets/restarts. I tried lowering details from all on max to disabling trails, shadows, long distance and quality of animations/characters/terrain. But it didn't help. I am using Shader 4. I didn't try to decrease shader to 2, like suggested in some other thread. Usually one core goes 90% when Regnum is running, always free 2GB RAM and FPS in game is 240-260. Regnum is configured in Firewall system.

Computer info:
Intel i5 760 (2.8GHz)
GTX 460 + latest drivers from Nvidia site
4GB RAM 1600MHz
Windows 7 64bit

Thanks in advance.