My IPhone 4 has the "black screen of death" and holding the power and round button isn't working, what now?

My iPhone 4 has the "black screen of death". I tried holding. the two buttons and waiting and waiting and waiting, but no reset, no apple, logo, nothin!

I've only read a few posts on this but almost all of them say this is the solution, however... its not working with my phone. what else can I do and still preserve.

the content saved on my phone? Most of my stuff is in the cloud but still.