eg. if the cultural dimension 'power distance' does not influence the relationship between usefulness and behavior intention, can we conclude that power distance does not exist in this case?
(1). It depends on how we measure the depth and level of usefulness. (2). Similarly, the stages of behavior- intentions vary among the beholders, and in measurement. (3). Our bias-ness influences the outcome. (4). The unit of measuring the power distance could vary based on the TSS-model (Time, Size, & Space) among different groups. (5). The conditions of A or B, as well as (A+B)'s relations could shift outcome. (6). "power" and "distance" exist.
I am not certain what you mean by "moderation," but if you mean in the "Baron and Kenny" sense (see below), then, no, that does not mean that "power distance does not exist." There could always be suppressor effects (see below). Furthermore, all associations depend upon how you operationalized your constructs (the measures you used) which have varying degrees of reliability and validity. You can state that with your data, and the variables you measured, on the particular sample that you employed, and with the statistical analyses that you used, there does not appear to be an association.
Good luck.
Baron, R. M., & Kenny, D. A. (1986). The moderator–mediator variable distinction in social psychological research: Conceptual, strategic, and statistical considerations. Journal of personality and social psychology, 51(6), 1173.
Zhao, X., Lynch, J. G., & Chen, Q. (2010). Reconsidering Baron and Kenny: Myths and truths about mediation analysis. Journal of consumer research, 37(2), 197-206.
Friedman, L., & Wall, M. (2005). Graphical Views of Suppression and Multicollinearity in Multiple Linear Regression. The American Statistician, 59(2), 127-136.
Are you using "power distance" in the Hofstede sense? If so it's a cultural value not a behavioural phenomenon - that is to say, a quality of a society with great vertical distance between the most privileged and the least privileged of its members (classes) and the extent to which this is accepted as normal, moral, justified etc. In Mulder's sociological variant, it indicates a type of organizational behaviour where if A has more power than B, they will try to increase their power relative to B to create a comfort zone (they may not always realise that that is what they are doing). B on the other hand will try to close the power gap with A, and increase it relative to any subordinates. If power distance (which exists anyway as it is societal) affects behaviour in your situation, it would depend what you mean by "usefulness" .. of what for whom? and behaviour intention - by whom? towards whom or what?