Hi @ted6641
had you tried using a different LAN cable and try direct connection to your computer? NAS >>> PC
is the speed still 100Mbps?
Try with another PC too.
Normally, for this case, I will try to backup important data, Connect to a external drive to the NAS USB port, login to DSM and perform file copy.
Check volume and hard disk health.
If still on 100Mbps,
you will need to inspect the board for any component or circuit trace burn / vaporized.
you need the right tools and equipment for component repair, some will suggest replacing the ethernet chip first.