That's a well known problem. SOMETIMES those Y USB cables help to get more power to the drive. LET'S BE CLEAR HERE -> USB powered drives are hit and miss. It's a known problem.
I've had a Simpletech 120gb External HDD for a few years now and just recently I began recieving the error message "Unrecognized device". In Device Manager, the HDD comes up as "unknown device". I've scoured the web for an answer but have found nothing.
I'll list my symptoms below if it helps:
When I plug in the HDD on other computers it works fine however on my laptop the red power light remains on but the blue "harddrive is working" light never flickers as it used to. When I plug in any other USB device on my laptop it works fine, it just seems to be my external HDD. The HDD does not come up in My Computer when plugged in after the laptop is turned on and when plugged in before starting up my laptop, my laptop freezes on "windows is starting up..." screen, or the External HDD comes up in 'My Computer' but when clicked on there are no files or folders.
I've tried everything with the exception of reinstalling the driver and purchasing new a new USB hub.