are the drivers installed through windows update? i dont know if this is the problem, but was the case for me with My T-Mo S3. Do this:
1)uninstall drivers via Control Panel.
2)Use USBDeview and uninstall any samsung related drivers like usb storage and what not.
4)Most important step: Disconnect from internet, and install these drivers Link Below.
5)KEEP Disconnected and plug ur device in and let it search drivers from HDD to force install instead of Windows Update.
5)Reboot, and you can connect to internet and should be picked up by adb.
Before trying any of this, is USB Debugging on?
|MG| USBDeview 2.16 Download
Download T-Mobile_t989_GSII_ADB_Drivers.zip from Sendspace.com - send big files the easy way