Hi, try this...
reset FW bus, same goes for USB reset...
Reset the Firewire bus
If your Firewire or USB isn't recognizing any device. A solution which has worked for some whose hard drive became invisible in 10.4 was simply to follow these four steps to reset the Firewire/USB bus:
1. Shut the machine down.
2. UNPLUG the power lead to the computer and any firewire/USB drive.
3. leave it for 10 minutes.
4. Connect back up and reboot.
Your new MacBook will not run PowerPC applications (those written to run on the old PowerPC G5 that you previously used) due to the lack of Rosetta in Mountain Lion.
Do you have the need to use any of these applications and if so, which ones?
Some here on this forum urge caution in using Migration Assistant from a PowerPC Mac to an Intel Mac. In my case, I only migrated my data files and reinstalled all of my Intel applications manually.
For general information about the migration, see this guide:
Is the drive connected via USB or Firewire?
USB and FireWire Quick Assist
What to do if your computer won't recognize a FireWire device
Dealing with FireWire problems (drives not mounting, devices unrecognized, etc.)
Common fixes for USB device issues (unrecognized, etc.)
Just wanted to say thanks to all for the tips and tricks.
I fixed it eventually. The culprit was a dodgy usb cable.
*Just a note to anyone who may stumble accross this thread: DON'T just try one alternate cable, I ended up trying 4 and fortunately 1 of them worked.
again - many thanks - I know know an aweful lot about FW and USB devices. ; )