My lacie big disk cannot be detected by windows 7 Professional (64 bits) if i connected using firewire 400 cable. however, no problem if i used USB cable. can you advise me on how to connect it using firewire 400 cable?

SOURCE: Two units conflict when connected thru Firewire 400

Windows XP and most pcs running it does not natively support firewire,as it was developed by Apple computers. Most Firewire ports on PCs are 4 pin. Your PCI card ( and I take it, its a desktop youre referring to ) should have a 6 pin connection. Firewire connections also have a 7 watt supply via the bus. You may need to open the computer and see if the molex jack on the card is being powered by your computers power supply. Two firewire drives, especially the power hungry Lacie quadras, may be to much consumption for the card. Hope this helps.

SOURCE: deference Lacie d2 Quadra1TB/Lacie big disk ?

It's all about the interfaces.
The Quadra has four interfaces: • eSATA • FW 400 • FW 800 • USB 2.0
The triple has all but the eSATA interface listed above.
For doing video work you want a big drive with a fast interface. If you have eSATA available then that's the fastest. If you don't then you're just as well off to go with the triple interface. The FW 800 would be the next fastest, then the USB 2.0, then the FW 400.
Because of the way that data is transferred I believe that when doing video work you would be best served by the FW 400 instead of the USB 2.0 even though the USB is faster I don't believe it is a full duplex communication so the FW 400 is actually better for video.

SOURCE: I had 4 LaCie 2TB Big Disk Quadra, Item 301343U.

Let's not take this as a solution so much as an intuition. I believe you may have run up against a limit of physical disk space that XP can administrate.

DO me a favor and don't give my rating a thrashing if I'm wrong.

Best Regards,

Marcus