Check the manufacturer's website for updated drivers for your firewire card.
Also, try changing the "allow the computer to turn off this device to save power" option on the Firewire Card's Properties Settings. If it is checked... uncheck it, if it is not checked... check it.
Start Button-> Control Panel-> System-> Hardware Tab-> Device Manager-> double-click your Firewire Card, select Power Management Tab
Also, you might see another option on this tab called "allow this device to bring the computer out of standby". Uncheck it, if it is checked.
Let me know how you make out.