I have searched him for a long time and i can't find him anywhere...i have searched in front of the Serpent Castle, the surrounding area and nothing...where the heck is he?? Can some 1 help me?

Kol appears only once prior to the Dragon's Spire: near the front entrance of the Serpent's Temple. If you saw him once there (or just walked by him) he'll be long gone now.

In the Spire you'll encounter him twice - the first time near some spiders and the second time in Erathsmedor's chambers.

Xignal

Welcome to the board, Qbas!!!

Did you by chance meet Kol once outside the front of the Serpent Temple and left before really talking to him? Talking to Kol outside the temple is a once only option. If this is what has happened to you - do you have a save game from before this point to reload? The only thing you get from Kol is the Heretic Key which gives you to a small room with a Statue of Kerah - there are some anhks in there and you can learn some more of the "story" but it isn't so significant that you can't just skip it.
If this isn't what has happened, Kol is found between the river and the Serpent Temple which is south of Ishad N'ha.

Hope you find him soon!!

Wyv