After attaching external USB HDD (no external power supply) OS can only see it as "unknown device" or can not install drivers for this device.
The above symptom may occur on the following systems:
All Idea Laptops
If external USB HDD has no external power supply it will use USB for this. USB is limited by standard to 0.5 A and usually that can be lowered a bit. Some external USB drives need more than 0.5 A and for that. In this circumstance,
1. you should either have external power supply or dual-USB wire that helps to get additional electricity from second USB port;
2. you should either try USB port on another side of laptop (maybe ports on one side of laptop have lowered currency) or use external AC for HDD (or dual-USB wire that should come in package with HDD).
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