It's all good. So if your still keen to troubleshoot (in either PC) this is the best plan.
Remember to turn the power off at the power supply switch or wall and wait about 30 seconds for the power to drain anytime before swapping anything but USB and audio cables.
Not doing this can damage the PC and cards and also give you symptoms that will mess up your troubleshooting.
Don't look at just booting your host OS immediately because it may reboot often and you can end up corrupting your OS and other adapters can be the cause of conflicts themselves.
With a PC using a minimal config is always easiest way to find hardware conflicts. Then once you know it's working you add things back until it "breaks".
So remove anything but the scsi card, video and keyboard from the PC.
Next make sure the scsi card can post repeatably without the scsi cable or drive attached and is stable in it's software. You do this to make a reference.
If it doesn't then you know either the card or the motherboard or bios memory is at fault adding the drive will not help.
So you must go into the motherboard bios in that case and disable network, controllers, audio etc etc. Which will free up hardware resources and allow you to get the card stable.
You may need to assign an IRQ to the card slot and also try the scsi card in another slot. If the card boots it does not mean everything is well.
With the termination you normally look on the external part of the card to see if it has a connector and work out by the model or in the config how many channels it has.
Some have one channel that would pass through so that means the rear of the card was one side of the chain and the inside of the card was the rest.
Some have one channel external and one channel internal. The reason you need to know this is termination. Which is a lot easier if you find the manual.
Either you will have to put on a terminator on the outside of the card, change a config setting, jump a jumper pin or if it's an internal channel it may terminate the chain at the card automatically.
Then you need to jumper the drive itself to use term power. If the cable is self terminating and has 3 connectors then you want to put the long end stretch to the card and the middle connector to the drive and leave the short stretch dangling as if it's a terminator its going to be there. Then you need to assign the ID. For more info check this out:
https://www.inkling.com/read/dummies-comptia-aplus-clarke-tetz-3rd/chapter-5/learning-how-scsi-worksYou will need to connect the drive (depower first) and see if it spins up and is stable. At this time you make a dos boot floppy with drivers and see if you can identify the partition.
Partition found then use either a software tool to read off the files or make an appropriate host OS.
Changing the drive to bootable is useful as it will use up more bios memory space and you may actually just be able to boot the drive on it's own.
Unless you know it's origins it could have anything on it.
If that drive has not been known running on that card before and the card is stable flashing the firmware can work. Never flash cards while they are conflicting in hardware unless all hope is lost.
This is most of the beginner stuff you need to know. It's the same troubleshooting no matter how old the PC is. Unfortunately there is no shortcuts.