I've got an external 240v 500gb HD. when it's plugged in (windows7) the computer recognises it and it is there but i can't access it no matter what i do. Any ideas?

Is it spinning up?
If you pick it up and wave it side to side it will feel heavier than normal because of the disc spinning. The gyro effect.

If it is spinning the. Check the connections, half a connection could cause the symptoms you describe. Better still un plug all of them and reboot. When your up and running again plug the exteral back in and try again.

If it still doesn't work try it in another computer to try and rule out any problems with your own pc or the external drive its self.

will do.

Drive is spinning, all been unplugged and plugged back. As i said it's there on the computer, i just can't access it in any way.

Right click on my computer...click on manage...then disc management...then right click on the hard drive...mark the partition as active and give it a new drive letter....if that don't work its goosed lol

I've got a feeling it could be knackered

Does it allow you to see folders ?
Does it allow you to see file?

Try it in another Pc or Laptop.
This will narrow down the fault.

It is possible that a Antivirus program is preventing access to the Drive.

I would say its broken if it wasn't showing up
But it is.

worst comes to worst, if you can see it, you may need to format it...