Okay,today i got home from school and opened my email,i see there an riot games mail saying that i broke summoner code and i got an account warning.

I got a link from them checked my tribunal case and yes it was a fair warning,3 out of the 4 games i had there were legit reports,1 of them was not i still remember i got trolled by a premade.

Anyway what i want to ask now is:After this my record will get clean?I mean if i start to behave and get good attitude ,stop beeing negative should i be oke?And never get that banned?Or is possible that are still cases made again against me from games past the one in the current waring?

I mean the next case will depend from the games that took place after this current warning or not more exactly the games that will took place from 13-11-2012?Please clear this for me,becouse this warning realy made me cringe and i realize that i want to get clean becouse i don't want to lose thousand of hours invested in my current account.

Nope if you dont break the summoner code from this point on you will not have any problems.

I apreciate your answer and i will try to keep a good atitude from now on.maybe a red will also confirm this

No need for a red to confirm, this ;D
If you try to always behave you should never fear to get banned.
Sometimes you can lose your head, but just try to stay positive, i have played for 3 years now and have never been banned, sometimes I have flamed people, its nearly impossible to never flame, but if you try to be constructive, you will probably not get banned. Losing your control is bad but it can happen for everyone, just don't do it to often.

If you follow the Summoner's Code there will be no reason to ban you.