interaction effects

Hello,

I need some help with my regression:
Crisis is a dummy variable which can be 1 (crisis) or zero otherwise.
I need to center my variable income on the interaction term because of multicollinearity

1. First I started running the regression without the interaction term and income is significant. When I included the interaction effect, it is not significant any more. Is this logical?
2. When I need to center the interaction term. How does it change my interpretation?
3 how can I include the interaction effect without multiplying the terms (is this correct: c.INCOME#CRISIS ?)
4 if my regression is transformed with the natural logarithm, do I calculate the average income using the geometrical average or the arithmetic average?

Thanks for your help.
Kind regard
Lisa