/etc/path_to_inst stores vital information about the devices on your system. If it is damaged or missing the machine will not be able to boot.

To recover you will need to boot off of a CD-Rom or the network, then mount your root partition by hand to copy /etc/path_to_inst back on there. Hopefully you will have a copy on a backup somewhere. I don't think just grabbing /etc/path_to_inst from another server or the CD will work. If you end up having to try that make sure at least you use another V490, hopefully one with exactly the same hardware inside it.

If that doesn't work you may have no choice but to re-install Solaris.

Good luck,
Ralph