it has been upgraded to win7, not by default when purchased, normally it's win 2k if i recall or w98
dont burn steps, grab everything here, theses where provided by TEK
https://xdevs.com/docs/Tektronix/TDS5000B/please do note this is a copy of the genuine site who ask registration by Xdev's, they have the same content, be sure you have a good cd-rom in the scope
unless you have nvram battery failure or other problem, even the computer cmos battery could have died and changed some of the motherboard settings ..