Several possibilities exist to explore such as:
1) What modules do you have installed in the chassis and what are the potential power requirements for the total configuration?
2) What are the power requirements (if any) for your sensors and attached devices?
3) Is it possible that you are trying to pull too much power from the SCXI backplane?
4) Do you know the quality of the power line you use as a source?
5) Do you need a line conditioner for your AC line?
I could try to help diagnose the problem, however, I will need a great deal more information. At the very least, I hope that I gave you some possible "paths" to begin your investigation.