I've tried all the obvious things (swapping out the PSU and the power switch, rechecking everything is seated and connected correctly, swapping out as many individual components as I can, etc) but I've hit a brick wall. At this point, I can only assume one of two things: either A) I'm a real dummy and I've missed something obvious (like consistently connecting the front panel leads to the wrong pins) or B) one or more specific patrts I've used is/are faulty. In either event, diagnosis at this point is beyond my ability.
Because I sourced the components from more than one supplier, it'd be a bit tricky to return everything, especially since I'd be required to pay for the courier if the parts aren't faulty, and even that wouldn't help if it's a user issue instead.
I've been looking around for local PC hardware repair professionals, and it's been surprisingly difficult to find someone. Few seem to advertise hardware repair, and fewer still want to take on a job looking at a custom built PC. At least one store I talked to insisted I send everything back to the manufacturer first before they'd even look at the thing. Some of the Google results lead to stores that no longer exist.
So can anyone recommend a decent PC repair professional on the North Shore (preferrably close to Devonport/Takapuna) or in the CBD? Ultimately I just need a diagnosis and I can take things from there (replacing parts, etc) but that seems to be the hardest thing to find right now.