Ok, so it is a 7043, 1 or F1 for SMS and 5 or F5 for a service mode boot.
Use the number keys on the QWERTY side of the keyboard for a serial / tty / dumb console and the F keys for a graphics / LFT console.
Try tapping the 5 key while it boots, this should bring you to the Diagnostics menu, then select Task Selection, then start a shell (I think - some one will correct me If I'm wrong) then import rootvg and edit the inittab to remove any applications, you may even want to stop mail, snmp, some of the IP related stuff for now.
Then reboot in normal and fsck, check no file systems are full, check the IP settings, etc.