I will post it because someone else can benefit from that solution.
I have 3 WD external hard drives connected to the PC trough a Belkin 3 port 800 fireware PCI card.
This setup works OK in windows vista. When I installed windows 7 the system became unstable, with repeated blue screens.
Thanks to the help of Jonathan I found that the cause for the problems was related to the fireware ports.
It seems the new drivers of Windows 7 are not working well with the fireware 800 ports. This is what I did, and it worked.
The 1394 bus driver that is included with Windows 7 replaces the 1394 bus drivers that were included with earlier versions of Windows. See this site for details
http://www.microsoft.com/whdc/connect/1394_Windows7.mspx
You can try the following steps to fix our issue, This solved my initial problems with a Maxtor III OneTouch drive.
1- Click the Start Button, type devmgmt.msc in the Start Search box and press Enter.
2- Expand the "IEEE 1394 Bus Host Controllers" node in the device tree on the right hand pane 3- Right click the host controller node select "Update driver software ..." 4- Select "Browse my computer for driver software" 5- Select "let me pick from a list of device driver on my computer ..." and Check the box before Show compatible hardware. 6. Choose the second option---1394 OHCI Compliant Host Controller (Legacy), and click next to update the driver.
The PC is working OK now.