To reset your sun ray terminal, simply press Ctrl-Moon (The ``moon'' key is the crescent in the upper-right corner of your keyboard).
If you don't have a Sun keyboard or you get no response from Ctrl-Moon, you can simply disconnect and reconnect the power cable in back of the sun ray.
Sun ray terminals can be reset or lose power without terminating your session or losing data. However, you may have to log back in to rejoin your session. Note that in some unusual cases, it is possible to set up your sun ray to operate so that you cannot reconnect to a detached session, but this requires effort and does not happen during normal operation.