PC Turns itself off

[Apropo]

OK I built 2 identical machines, installed them the exact same with the exact same parts.

i5-3570k
8GB 1600 Corsair LP ram
GTX 670 Gigabyte Windforce OC edition
Samsung 830 SSD
Windows 8 release preview

Until today they have both been working perfectly. One of them now when we go to a specific website turns itself off. On the other machine I can go to the same website and it doesn't turn off the computer. The computers are brand new and super clean. They have tons of ventilation and the temps are normal.
What could be making the computer restart only when going to that website?

Thanks for the help.

EDITED:

We've tested the computer now for over an hour, it doesn't restart itself off. We go to that specific website to log in and as soon as any number is pressed on the num pad of the keyboard the computer shuts off.... WTH!?!??!?? Tested further and pulled up the calculator and as soon as any key on the numpad is used it turns off the computer?????

 

[Apropo]

I'd still like an idea of what would cause this but as it stands, I didn't change anything and it seems to have fixed itself :/ (so confused)

 

[jsc]

Try swapping keyboards the next time it happens.