UNIX for Dummies Questions & Answers

I am new to unix and have questions. We have a older SGI box that boots only to single user mode. I beleive it is doing that because of a failed fsck. The unit passes all hardware tests on boot up but gets to "starting up the system" and fails with the following: "init cannot create /var/adm/utmp or /var/adm/utmpx ran out of disc space" then I have the option of "crtl d to complete normal startup" (this just loops) "or give password for single user mode" Don't know the root password. So in researching this it appears that I can boot to another drive, modify the passwd file to delete the encrypted password, reboot and repassword and then fsck can run and all is good....The problem is, what are the keystrokes to do this? I have zero unix experiance. Also it appears that no recovery discs where ever made. The system id comes up as "IP27 prom SGI v6.64 02121744 system V" Does any of this make sense and can anyone help??

I assume from the number of views but lack of responses that everyone thinks this is a hacker question. It is not. We own the box, can prove it. It is a Reynolds and Reynolds dealer management system for automotive retail use. We own the equipment and have Reynolds permission to use the software, they just will not assist with any diagnoses or repairs. Please let me know if anyone can help or at least point me to a resource that can.
Thank you