First hello to all & many warm greetings from sunny Split, Croatia

Well, as I'm so new & fresh in web developing I'm desperately begging for HELP!!!
I have this site for administrating and the problem is that all works just fine until resolution get higher then 1600 x 900.
Then whole page become very ugly. All elements become displaced.

Please can someone help me to fix this problem?

Tnx in advance,
Frane aka. Vitriol

I hope that I ask this question in correct place.