boot load failed

I modified the partitions on my Solaris 10 disk using format command in "boot cdrom -s" mode and then tried rebooting with "reboot". It said "Boot load failed".
Why does this happen?
I have faced this error before:( and I went in for a fresh installation of the OS.Can anyone tell me the reason as to why this happens?:confused:

you can't (without problems) change the partitions after installation! to do something like taht you need a second disk and use liveupgrade ("lu"). maybe, if only your bootsector is missing, the command "installboot" may work...