I had booting problem last week. After grub screen, screen was black and later reboot. First I try rebooting verbose mode editing line in grub "kernel /platform/i86pc/multiboot kernel/unix -v"
How to Modify the Solaris Boot Behavior by Editing the GRUB Menu --> http://docs.sun.com/app/docs/doc/817-1985/fwbme?a=view
Then I got:
/boot/solaris/bootenv.rc - line 23, syntax error.
first we edit bootenv.rc
setprop console 'ttyb'
setprop console 'screen'
I could proceed with pressing ctrl+d two times (which stops running script at that time). So I could proceed with booting.
This is a bug related to kernel. Probably kernel do not show boot process to screeen. Also some boot scripts which gets information from eeprom (related to boot-args) hanged. In that kind of situations Ctrl+d could be good solution if you belive scripts hanged during boot.