I have Samsung dues phone gt-s6802. Under windows 8.1 it is not recognized. but if it is connected before power on of the system or shut down computer and reconnect the device then windows 8.1 is also recognized it. May be this info helpful for someone else. thanks.
I have installed windows 7 and 8 both. There is no issue with windows 7. The same problem I have faced with previous PC. I have installed all drivers as well as KEIS from Samsung and did all type of experiments with phone and pc for approx. 15 days. This shutdown trick was found sudden but works. Thanks for your support and guidance.
wait i remember part of the issue.. itunes installed ? disable auto sync in its settings and close it.. now in the start screen (or hold Win key and F and set to search in Everything) type autoplay to get search results then find the Green iconed result click it. at the bottom of list in devices change to: do nothing.. or select kies. dont forget to do optional Windows updates ..