Seems to me you are not alone in your experience with KIES.
What is happening to you, happened to me.
KIES just goes into a an endless loop of "connecting device".
During this, no USB connectivity was possible.
Here is what I tried:
1. disconnect GS from KIES - reconnect - no success;
2. disconnect GS from KIES, shut down KIES - reconnect - no success;
3. shut down KIES - shutdown GS, started up GS and reconnected - KIES looped - no success.
4. instructed KIES not to load device upon connection - KIES ignored the instruction - no success - still looping.
5. whilst GS disconnected - uninstalled KIES - shutdown GS - powered up GS - connected via USB - SUCCESS for USB connectivity (immediately).
Whilst KIES is good for managing contacts, it's current instability will have me avoiding it's use.
Just use windows explorer via USB connection (but uninstall KIES & power down/up GS first)