Bro, dun need to factory reset. I just did this.

http://forum.lowyat.net/topic/2104508 (Page 1 > Post 3 > Q.21

Resolution

1. Unplug the USB cable


2. On the cell phone, dial the following number: *#7284# Once the last # is hit, the PhoneUtil application is launched. Choose USB -> Modem and then USB -> PDA mode. The good mode should be PDA. Even if the mode is PDA, switch to Modem and then back to PDA.

3. Plug the USB cable.

Note:

* Repair USB connection for any Samsung Android phone

Reference: http://www.youtube.com/watch?v=KV2h5O_qDPE