I had the same problem about two years ago. I believe I used what this
post says:
http://sunportal.sunmanagers.org/pipermail/summaries/2003-October/004407.html

Crtl #

Brock

On 8/23/05, Brent <bfriedman at exstream.com> wrote:
>  
> I have a problem that I thought someone might have experienced before.  I am
> trying to get the machine to boot from an install cd, but things aren't
> going as planned. 
>   
> I have a sun blade, with only USB keyboard/mouse input.   It is currently
> running solaris 9, but it is flaky - meaning, when I try to open a shell
> console, CDE gets a black background, and no shell opens.  The mouse and
> window manager remain responsive, but I can't get to a shell to init 0. 
>   
> Since there is no sun keyboard, stop-a isn't available.  Ctrl-break should
> work, but it isn't working via the usb keyboard adapter. 
>   
> I tried the 'hit the power button after initial beep,' but that doesn't get
> me any closer to an openboot prompt. 
>   
> Any ideas? 
>   
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>