So when you say "I changed the PCI 1394 and jack" do you mean you physically swapped out the firewire adapter (and cable) for another one?
Losing audio and/or MIDI sure sounds like a bad firewire adapter or cable, or possibly a bad firewire port on the interface.
Do you have any other firewire devices plugged in, like a camera or external disk drive? Is the interface powered through the firewire port, or using its own power supply? When the interface goes dead, are all the front-panel indicators still lit? Have you checked if there is a more recent driver available for the 003? Are you sure the driver version you're using is Windows 7 compatible?
If you've changed the adapter and cable and are still having problems, then it would seem the prime suspect is the interface itself. Sadly, prosumer devices don't last forever (fingers crossed, my MOTU is still going after 8 years).
I have experienced similar problems in the past. This may not relate to your situation, but in my case it turned out to be heat-related. I was not in the habit of turning my interface off - ever - and it happened during a period of very warm weather. I'd lose audio, and sometimes could get it back by unplugging and re-plugging the cable, but most times I'd have to reboot. Since then I shut the interface off when not in use and haven't had that problem since.