firmware upgrade encountered an issue, tried many options, but still stucked. topic

hi,
i was using my galaxy ace without rooting. once I switched it off, and tried to switch on, i found it stucked in the bootloop. then i tried factory reset/wipe user data and wipe cashe partition with the stock recovery. But it didn't help. it was showing process completed wthin 2 seconds. so i'm not sure if that process was actually completed. Anyway, it never helped.
then I decided to flash stock rom with odin. i tried to open download mode by pressing vol down + home + power button. but then i found that even download mode is not opening. then i searched over internet, and found a tool, 300k tool, which really helped me to get into download mode, and somehow i started flashing stock rom. But unfortunately it failed, and left screen with a error message "firmware upgrade encountered an issue. please select recovery mode in kies and try again"
then i installed kies, but my phone never connected with usb cable. it keeps showing that its connecting, and at end it shows a message that says reboot device. but rebooting never helped.

now i really dont know what to do. please someone help me.
thanks in advance :)