Thanks so much. I can confirm that I did indeed flash a rom which was intended for i9000 on the i9305, and have lost my IMEI number and USB access.
Edit: I just followed the last part of that guide you linked me to eariler. I did the option titled, "Recovering IMEI And Data Connection After Flashing WRONG Root Package Intended For I9300".
My network is now working and so is my USB cable.
When I flash the stock rom, will this mean everything custom I did will be wiped, all that junk I modified and did by mistake? I want a clean, fresh install. And the link you gave me, which one shall I download? Before I rooted my Android version was 4.1.1, but on link you gave me there is 4.1.1 Decodex and Codex, which one shall I download?