Lacie HArd drive not accessible

I have the same problem too on my 2big form lacie . If I use 2x 1,5 tera disk in "fast mode" or in "big mode" my disk manager only shows 746 gigs available (it should be at least 2,5 terra).
If I use "safe mode" so my system can see 1,3 tera available, wich is normal for a raid mirror configuration.
I hope to find a solution quickly.

Did you check the MS hardware compatability list http://www.microsoft.com/windows/compatibility/windows-7/en-us/default.aspx

1.
log onto d computer as administrator
2.
start->my computer->manag
3.under storage->disk management
4.ef intialize ndcovert disk wizard appers click next ef not skip to step 8
5.on d selct to disk intialize page click next
6.on d select to disk covert page click next
7.on completing dhese two click finish
8.right click u r external drive nd click format
9.in d format dialog box type d name for u r external hard drive nd then click ok
10.click ok again

Try connecting the Lacie to another computer, if it doesn't work then the hard disk may need to be formatted using Disk Manager. I suggest you format as a primary partition in FAT32.
If it doesn't work then it is possible that the hard drive in the Lacie has failed.
To test the hard drive, remove it and connect it to an USB hard drive adapter and connect it to a working computer's USB port. If it deosn't detect it as an external drive and you connot open folders and files then it is faulty.
You can install a new hard drive in the Lacie and then format in FAT32
There are companies that can recover data from faulty hard drives BUT it will cost you an arm and a leg for their services.

Go to computer Management, change the drive letter from F:\ to any letter.

You will need to format the device for Windows use. If you can see the device in My Computer, right click it and select format. if you can't see it in My Computer, you will need to use a boot tool such as Gparted: http://gparted.sourceforge.net/download.php
Download the .iso file and burn it as an image to a cd, then boot from the CD at startup. It should detect the 500 Gb drive and allow you to format it to NTFS. Then Windows will recognize it.

i use my external hard disk many times but now when i connect my lacie external H.D to PC it dose not recognized

try restarting you rcomputer

Listen to your power supply and see if it is making a faint buzzing noise. Try your device with a new power supply. With a new power supply my drive now runs fine, and was not corrupted.

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