linux - Accessing computer with GUI turned off -

my father, rather unexpectedly , sadly passed away, had old linux computer used access remotely (perhaps via telnet?) on our local network tablet.

the computer still running , access it, fearing if shut down , later restart it, not able due password restrictions.

i have, of course, physical access computer, gui seems disabled because when connected monitor didn't signal. don't know ip-address of computer , don't know password our router, otherwise have checked it.

any suggestions?

edit: in response downvotes, not think trespassing or violating privacy. lived together, , used share passwords me don't think there's terribly private on computer. might try passwords remember, might have forgotten right one. afraid turn off computer , kill current session, seems not result in loss of significant.

my condolence loss.

first ask if want dig late father's data (and privacy). , might not able useful it...

then, supposing have basic command line skills on linux. if don't, learn them first (on own machine, perhaps in vm). takes several weeks.

many linux machines don't have gui, since accessed command line interface (a typical example of course vps hosted elsewhere), using ssh (telnet out of fashion, , can't imagine father used that).

most desktops can physically reset (by switch on motherboard) clear bios password, etc... might need that. boot linux usb key (and won't harm data on disk, if careful enough).