Unable to shutdown and start machine

Hello.
I have just installed solaris on my PC (standalone). It allows to reboot. But IF I shut down and the restart by pressing the button - It does not show my solaris OS and I am then forced to perform fresh installation.

Could you please let me know the fix for it - So that shutdown and start works as restart works.

Thank you!

How do you normally shutdown?

shutdown -i 5 -g 1 -y

I had done below to shutdown:
Click on launch button...then Shut Down radio button... Isnt it correct way to do that? Then I used to press the CPU button to start and found all gone.

Should this command' shutdown -i 5 -g 1 -y' be supplied from unix prompt? How must I start then?

Yes, as root.

Start what? The machine or a unix prompt? To start the machine the power switch should do the job, to start a unix prompt either ssh into the box or run a terminal from a graphical desktop.