I have a 120gb usb after connecting it in pc it

Probably not an issue with the MacBook but with the Pleomax drive. Be sure the drive is getting enough power to begin with. If it came with a 2 headed USB cable be sure to connect BOTH USB connectors to the Mac. You may also want to try the drive while your COMPUTER is plugged in and charging. Laptops and external drives don't always get along due to power differences and specifically laptops who do not want to waste their battery power on an external drive. If all else fails, try the drive on another computer just to make sure it is a drive problem and then contact the manufacturer for a repalcement drive.

u might have to format it in safe mode or buy a new one, if you try it on some one elses comp. and it works it ur comp. but it is most of the time a software issue

Buy yourself a USB to IDE & SATA disk adapter from eBay fro a few $$$. Then open the Tosh case and unplug the drive and power supply connectors and remove it from the case - carefully. Plug it into the USB to IDE /SATA adapter and lay it flat on a non conductive surface and connect the USB to your PC should see it as a new drive. This will allow you to get the data off the drive, check for errors and reformat it. If you can’t see the drive from the PC then it is likely that the drive is fatally faulty.

It is your driver related issue.
Check your operatign ssytem version is winxp sp2 ?
SP2 is perfact for usb 2.0
Also you can try to uninstall all usb driver and install inf update utility it is comes with motherbord disk.
You can uninstall usb drivers from computer with device manager .
For that go to my computer proeprty then hardware then device manager then uninstall all usb drivers.then restart the computer then check.
Also check your harddriver usb cable is working fine tryt all usb ports of computrer 1 by 1.
Also try in another computer.

To isolate the problem, please try the steps below:

1. Make sure that the USB ports of your PC are working.
2. Try to connect the device into different USB ports.
3. Try to connect it into different Windows based computer.

Question: Did you reformat this device using your Mac? If yes, there could be a possibility that the device was reformatted using the Mac OSX (Journaled). This type of format would only recognized by Mac computers.

But if it's formatted using the DOS based system, it would work on both Mac and PC.

Unfortuntly, this caused the drives power source to be exceded and damage the drive or circut board. If you know someone that knows computer well, have them or yourself take the hard drive out and manually connect the driver to a computer and extract your data, if the drive is not damage that is, there is know way to know for sure until you try to connect to a PC directly. Or, purchas another USB external housing.

Does you drive make any sounds like these? If yes you have a mechanical problem and you should get a specialist to work on it.
If not - try to remove the drive from the enclosure and connect it directly to the computer to recover your files.

Try THIS link..

Is the drive partitioned and formatted already?
Does it work on another computer?
Is the drive powered via the usb cable, or does it have an adapter?
Do you have any networked drives on this computer?

When it is connected on your computer,
click Start
right click Computer
click Manage
double click Storage
double click Disk Management

Is it in the list of drives in the lower half of the window?

Is it of the same config? Are you hot swapping while the network is active? Do you have any redundant drives on the server?