On a related note, if you don't make a backup of the /etc/system file, you can tell Solaris to use /dev/null as the boot file. That should allow it to come up with a very vanilla kernel- enough for the box to come up so you can fix the broken /etc/system!
'psrinfo' will provide whether the processor is online or not. 'psrinfo -v' will give extended information it's status, speed, and other items. Helpful if you need to order a replacement CPU.