I recently bougth a new 250gb hard disk for my mac so i bougth a external usb drive case for my old 80gb seagate drive.
The disk case i bougth was working fine with the exception that ocasunaly it whould "drop out" for a few seconds..(just like if i manualy removed the usb cable) I understand that it happens because usb power is not enouth.

The case did not came with a power adapter, but i came with one of those "2 to 1" usb cables but i cant use it cause i need the other usb, so i bougth one of those universal power adapters, the case requires a 5volts adapter, i could not find one so i used a 4.5v adapter. (i can also try 6v but im afraid i will burn the drive)

After i tryed that my macbook does not reconize the drive anymore, i also have windows installed on my mac and its also not reconized in windows.
After that, i tryed the drive on another pc and it works fine,
and i tryed to plug other usb devices to the mac to see if they are working and they are.
Can anyone help me please?
Is it possible my mac blocked that especifc usb device because of some eletrical issue?