In SI, just two days playing there but all the guardians want to kill me! i can figth against one...maybe two...but when in the castle, lot of them appears and i can not get inside. Why?

You accidentally stole something? You will have to serve your time. All your weapons and stuff are taken, you're placed in a cell, and if you fight your way out of the jail, all your stuff will be in a chest at the exit.

Regardless, this is an excellent excuse to justify your newborn homicidal career, do not waste more time, kill all in your way.

Then leave the SI and continue that in Cyrodill. Blame it on the "island's maddening whateverness".... No one will argue.

I assume that by guardians you mean Dark Seducers and Golden Saints?

Did you break the law somehow? They'd attack you on sight if you have a large enough bounty on your head, but I think you might have noticed that you broke the law if you did something to get your bounty high enough for attack on sight-behavior... Check if you have a bounty on your head, and if you do you can clear it by joining the Thieves Guild and paying it off to a Doyen or by serving your time. Just yield (block key + activate) to a guard and they'll stop attacking you and arrest you.

Shield and activate at the same time when you're fighting one. (The should stop attacking you since their gaurds)
Then that should make them less hostile, but I'm afriad they might talk to you about going to jail. Before you do so, you should take all you items off you, so that when you're sent to the dungun you don't have you go to the evidence chest to recover all the items and you can just leave. (: