Hi QuirrelJibbly,
It shouldn't matter if you use your Neutron in its own casing or in a Eurorack casing. Of course you need to check that the power cable has been connected correctly on both ends i.e. on the module/Neutron itself as well as at the bus board. If I remember well then the Neutron has a boxed pin header so there the problem shouldn't occur however if you have a non-boxed pin header bus board, then there you have to be careful.
Other than that, the Neutron should just work in your rack. Keep in mind that it takes 1 A or 1000 mA from your +12 V power supply so make sure that you have that power available. So perhaps to get started put the Neutron back in its own casing and try to use the outputs VCF1 and VCA, they should work properly. Once that works fine and you are still convinced that you want to rack your Neutron in a Eurorack case instead of in its own case, then transfer it to the Eurorack. If it then doesn't work any more then there is something rotten in the state of Denmark. So either you wrongly connected the power cable or you are beyond your maximum power consumption for the +12 V!
Good luck with the troubleshooting and please let us know how it goes. Kind regards, Garfield Modular.
For review reports of Eurorack modules, please refer to https://garfieldmodular.net/ for PDF formatted downloads