I've got 3 hard drives (with power supply, USB 2.0 and 3.0). They are all recognized by Windows7 x64 when they're plugged in individually, or when 2 of them are plugged in at the same time (on any of my 4 laptop's USB ports).
However, when the 3 of them are plugged in at the same, W7 only detects the 2 first ones plugged in.
I also tried to plug them on a hub (which has a power supply) and it gives the same result.
When the 3 of them are plugged in at the same time and there's 1 or more pen drives plugged in, only 2 hard drives are recognized but all the pen drives are recognized as well...
Anyone might have a clue why that's happening?