It is possible that a sudden loss of power is causing the HDD to shut off during operation that causes the HDD to click. Therefore the click is an effect not a cause. If this is the situtation the problem will be found in your new DC connector. You should get that sorted before using the Laptop any further as you may well damage components.
If you want to eliminate the HDD as a potential cause then remove the HDD and see if the Laptop will post. Of course it will halt when it finds no boot drive but if it stays on without shutting off at a BIOS level then it will likely be the HDD.
I would think it is the first scenario and potential for damage is high.