Samsung Galaxy S i897 not detected by PC
Apart from potential issues from your current OS version, installed drivers, etc, you can look at this problem from your phone's side.

Assuming that the problem doesn't lie with Kies, Windows 7 or the drivers in use:


Before connecting your phone to the computer, open the keypad and dial *#7284#;
You will see a menu for UART and USB;
Under USB, select PDA. If PDA is already selected, select MODEM and then back to PDA;
Don't worry about USB debugging or anything, just connect your phone to the PC
Everything will work as it is intended to whether you use Kies, no Kies or just Mass storage.


This is a known problem with Samsung, the PDA mode for the USB connection needs to be active. And when active, sometimes we need to reset it by selecting something else and then PDA again.