Difficulty installing from sd card

Hello to all.
I just recently a BBB A5C and connected to the PC everything works perfectly.
After some tests I tried to install UBUNTU MINIMAL but without success:
Download the image file.
Writing to SD 32Gb class 10 with Win32diskimager
Inserting SD BBB with no power
I press on button boot
connect 5v
And after a few seconds, release the button boot
… but nothing happens … after one or two hours nothing
The 5 blue LEDs do not remain permanently on and the new system is not installed.

What’s wrong

regards Alberto