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
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.