From the debug page you need to enter these cmds.
Andy's Favorites
The debug screen can be reached here
https://IPAddress/admin/debug.cgi
df -h/ <enter> (this gives you file system info)
touch /nopivot <enter>
Now reboot the server it will bring up the maintance screen.
The OS upgrade will allow you to reinstall the OS, same version or newer. But will not allow older versions to be installed. But it's not a clean Install. Clean meaning that
ALL DATA will be lost. The above cmds will totally wipe your HD's according to Andy. I have not used these cmds but I believe Andy when he say they work. He has used them many times as he repairs and upgrades machines.
As long as you can remotely access the Server these should work. For conformation wait for Andy to respond.