If you're sure the substitute power adapter was a compatible one and working properly there's nothing for it but to take it apart.
I presume no lights come on and there is no sound at all when you turn it on. Most probably a fault in the power supply section. There may be a fuse inside which you can replace, though if it's blown at may well indicate some other problem which caused it to blow.
Look for any signs of overheated components. Also look for swollen electrolytic capacitors (see https://therestartproject.org/wiki/Basic_electronic_components#Fault-finding_and_Repair_3). Look for the rectifier diodes (https://therestartproject.org/wiki/Active_components#Diodes_and_Rectifiers) and test them with a testmeter.