I tried to install windows 10 and now my computer won't start

[Pierre-Olivier Gagnon]

I received the notification to do the free upgrade to Windows 10 and I started installing it.

It seems like there was a problem in the installation because now my laptop won't start.

I have a Toshiba Satellite and when I turn it on, I see the Toshiba screen loading but after 30 seconds it shuts down. I cannot do anything with it.

What can I do