Hard drive icon wont appear on desktop

Try a different USB jack. If it still doesn't appear you probably have to format it for Windows.
To do this, right-click on My Computer, go to Manage, then choose Disk Management.
The disk should appear there. You'll have to format it for Windows in order to use it.

First cehck whether your computer is able to recoznize other USB storage devices or not. If you see that it is not recoznizing other USB storage devices. Then you need go to your Boot Up screen, the screen that opens when you restart your PC.

Then go to the USB section and enable USB drive.

If this also does not resolve your problem, then try installing USB drivers on your PC, You can install them from the website : http://www.softwarepatch.com/tips/usb2-driver.html

I hope this resolves your problem.

We have a few of these Lacie Design by F.A. Porsche 500GB drives in our office. Our editor's drive stop working this morning (was fine the day before) and had all her files backed up from the last three years on it and was making a very soft clicking sound. After taking the whole thing apart and trying drive in another F.A. Porsche caddy with no success, we tried a different power supply hey presto it started up no problems. My drive that suddenly stop working earlier in the year we tried a power supply from a external Lacie DVD Writer and again drive is working. Just to make sure tried the original power supply and would not mount. So if your hard drive stops working it maybe the power supply rather the the hard drive.

I have the same problem, it was working but just stopped for no reason, even tried new leads but still no joy.

Here is the support website for the LACIE products.  As far as I knowthis site simply answers questions. Sounds like the hard drives are bad to me. 
http://www.lacie.com/support/

did you check the jumper settings.

You can try buying a new HD enclosure, then removing the HD from inside the one you got and mounting it inside the new one. Try also disconnecting completely the power cable from your computer for five minutes and then plug it back to the power and restart it. I know it sounds weird, but sometimes usb mass storage devices suffer troubles caused by electrostatic charges.

Hope

try going to the manufacturer web site for the make of the hard drive
find a download for that model and select mac as the operating system\
download and run

have you had this drive long if new then go to the control pannel on the mac and find the Amiistrative Tools open then computer managment open then Disk Mangement then open and find the unallcated drive then properties then partition format partition then go to nxt step then follow till end excepting all defaults as hdd is formated for pc not mac so id is needed to be reconised on mac. close all windows then in my computer you should now see hard drive letter if not turn off drive then return on.

if it is a USB (or you have low disc space), it does take longer to show up on desktop and patience is required... on my iBook it takes over a minute for my Brick to show up... Whether it is USB or firewire, do try another cord (I had similar problem with my lacie firewire external... I used a different firewire cord and all was fine. If you have tried these already, I hope you find the answer... good luck