mobile

My problem: samsung galaxy s2 gt i1900, rooted for the first time yesterday by someone not so experienced (me). After rooting, it worked well until I did a factory reset from phone menu. After that, it got stucked on boot, samsung logo with the yellow triangle. It only works now in download mode - I cannot acces the reset/recovery menu - it restarts over and over. Odin recognizes the phone.
I have read many threads here [URL="http://http://forum.xda-developers.com/sitesearch.php?q=samsung%20galaxy%20s2%20stuck%20o n%20boot%20after%20root"] , but I didn`t find a real step by step solution. Could be my fault. Anyway, I need your kind help before making another wrong move.
From what I understood so far, I could download the original firmware from : www.sammobile.com, then Download mode - Odin - PDA - load the original firmware - start. If this is right, I have a few questions:
1. In odin what options must be un / checked?
2. After this step (if I`m right so far) can I still root the phone after fixing the problem? If so, please recommend me a safe firmware. Or if it`s possible to load directly a custom rom (not the original one but a safe, working one), please tell me (link).
If I`m wrong so far please teach me how to fix this frustrating issue.
Please excuse my english and thank you.