Hi..you seem to have a problem..so let's see if i can help..first off did you at least write down what your original firmware was.. if so you will need to download it again as you will need to reflash you phone..
if not then you will need to check the pages listed below to find your firmware for your phone and the region that you in..
you can check here..
SamMobile Firmware Page or
[ROM+Guide]Official i9100 Firmwares K/G/H/I/J/KK1/2/5/KL1/2/3/LA2,4/LB2 Download - xda-developers
not a 100% sure if Intratech has all his links up yet but you can check plus read the first few pages as it pretty hard to brick the S2..and most/all of the information you need is posted there
you will also need to down load Odin3 v 1.85..to flash your phone
(make sure that you don't have kies running in the background as it doesn't get along with Odin,bring up your task manager and end process with anything that says kies )
take the firmware that you downloaded and place it in a folder on your desk top so it's easy to find ..
extract and start odin..and look towards the lower right side you see where it says bootloader,pda ,phone and csc..
1) check the pda box then hit the pda square to find your downloaded firmware (this is why I said place it in a folder on your desktop)
2) put your phone into recovery mode (hold the power button, volume down and center key ) and make sure you have at least a 50% charge on your battery..
3) connect phone to your computer and give Odin a minute and your ID:COM will turn yellow when the phone is connected (if not then check your usb drivers for your phone)
4) then press the start button and let Odin do its thing will take about 3 to 5 minutes..if all goes well you will get a green box saying passed your phone should automatically reboot and you'll be back to your original firmware..
after you done this drop me a pm and we'll get you rooted or just follow the directions in Intratech's post to get rooted.. feel free to drop a note if you get stuck some where..good luck