Measure the voltages at the Molex connector. Some of these external adapters have power supplies which are not well regulated. I have seen many overvoltages which have resulted in shorted TVS diodes on the HDD.
A cheap digital multimeter should cost you around US$5 and will be very useful around the house and car.
Thanks for your response.
I don't think there is a molex connector here unless I am missing something. The external drive which has stopped working is an IDE drive and it is connected with the power supply and with an IDE to USB connector. I don't see any molex connector.