Desktop computer does not start

To whom it may concern:

I have an old desktop comptuer (purchased 09/2008) with window vista op.
On last Thursday, my son shut it down. Since then, it will not start.
The power button shows 'orange' color after I press the power button.
Nothing happens, the color stays the same.
If I press the power button one more time, the color stays the same and nothing happened.
If I press the power button longer, this shut down the comptuer.
Any suggestion ?

Thanks in advance for your helps.