MacIntosh Performa 6400/200 Manuals

The manual contains information about troubleshooting and software (re)installation.

http://download.info.apple.com/Apple_Support_Area/Manuals/desktops/0300027APRF64 00UM.PDF

You may want to check the internal 4.5 V alkaline battery. A bad battery can cause startup and video problems with some Macintosh models.

Do you only want to read the files directly from the 6400 or do you need to copy and transfer them? In the latter case, how modern is the computer to which you would be transferring the files? Other than attempting to connect it to a network, file transfer to an external medium would be necessary, such as floppy disks or a SCSI-connected device (hard drive, Zip drive, or CD-R/RW). You can purchase an external floppy disk drive that connects to a USB port and can recognize high density 1.44 MB disks, but not the double density 800K Mac-formatted disks. If the 6400 were running OS 9.1, you could install a USB PCI card and transfer files to a flash drive, but that involves too much time and effort. The easiest and least expensive solution would be removal of the front cover from the 6400, so that you could access and remove its internal IDE hard drive and connect it to a USB-to-IDE adapter. These adapters aren't Mac-specific, so you can purchase one from any PC computer store or electronics store. The adapter converts the hard drive's 40-pin data interface for connection to a USB port and includes a power supply for the drive. Reviving the 6400 can be troublesome, especially if it has sat disconnected from electricity for a long period of time. If this has been the case, you can be sure that the internal 4.5-volt alkaline battery (Rayovac 870 or 871) on the motherboard is dead. Of greater consequence is the possibility that the battery has leaked alkaline solution on the (vertically-oriented) motherboard and corroded the components that are situated below its mounting position. Those alkaline batteries were notorious for leaking when dead and ruining the motherboard, when the corrosion was extensive. I always removed that style battery from the Performas having it, prior to storing them. Post back with details about what you hope to accomplish and how much effort and/or expense you're willing to put into this project.

That is tricky. The 6400 was a funny beast of a machine. It was among a series of Macs which needed a CPU firmware test to verify if it could run Mac OS 7.6 or above.

For many of the old knowledgebase articles this guide will be helpful finding old documentation:

Knowledgebase links of the info.apple.com format no longer work

And here is how to find old Mac downloads:

How to find Mac OS 9 downloads?

Apple never made free license use for Mac OS 7.6 or higher. So you should have the original CD or floppies that came with your computer. They are hard to find.

http://www.lowendmac.com/ has additional resources.