When you say "come back the next day...", do you mean the system is left on overnite? If yes, I would not do that(and you KNOW that SLEEP and HIBERNATE modes are not recommended, right?
). If not, then its probably the old beast(the 002) is signalling its unhappiness with the living world and wants to retire
Given the age of it, and the known issues with the power harness and PSU, I would consider a modern replacement. A-its going to sound better, B-its probably not going to quit working on a daily basis, and C-its likely to have more IO in the same(or less) space
Could it be the FW? Maybe, but if you have the latest(and correct) driver, its not likely(but if its a separate card, I would pull it and re-seat it a couple of times). I would also re-seat the power harness connections(5-6 times for each connection) to see if that helps(its free and won't hurt anything).
If this is the only issue you have, you could always simply add a decent USB-MIDI interface to cover MIDI IO needs(I am very happy with my MOTU Fastlane USB 2x2)
