I normally use Chrome. My second computer, a laptop, is running the same Win7 Ultimate. I can log-in successfully on the laptop but cannot stay logged-in on the desktop with any browser. I have tried it with Chrome, Firefox, Oprah, Palemoon, Safari, and IE. All of them give the same results even after clearing all history and cache settings.
The only difference is that that the laptop is connecting to the router wirelessly and the desktop is hardwired to a port on the router.