you might want to check your event logs.. most of the time they will mention what caused the restart.
go in cntrl panel, admin tools and event viewer.. i would start with system.. looking for red icons.. and then I would check application. most likely something that caused a reboot will be listed in system
you got some nice ram and cpu there.. I take it this was your main system before mining?
what did you use for video before?
Did you uninstall that video cards drivers before shuttng down and taking it out?
did you use a driver sweeper?(get a good one from guru3d)
also might want to make totally sure the cards are seated all the way in.. and yeah power supply voltage swings can cause it as well.. might want to monitor voltages and post them here, so we can see if any are out of spec.
I checked the event logs, and they don't mention what caused the restart. It only says that my system has been rebooted without a proper shutdown and can cause serious damage.
I bought the case, mobo, chipset, ram and hdd from a friend. Then I bought 2 brand new 5870's to start mining. I also bought a brand new 750W gold cert PSU. The hdd has been formatted and I freshly installed W7, gpu's (crossfire) and used the ati 10.7 drivers (the newest drivers cause a slight lower Mhash/sec).
How can I monitor the voltages? I guess the voltage swings are causing the reboots. But it seems that if I don't lock my system (windowskey+L) the system doesn't reboot, but if it's locked for a while, it seems to reboot from itself. Strange!