Thread moved to Multimedia & Video.
Can't boot machine, blank screen, hardware failure, unusable system. That's urgent. Most the posts here; urgent. The majority of posters here would consider their issue to be urgent.
Consequently, I have moved the thread and changed your thread title to something more descriptive of your issue in the hopes you might have a better chance of getting support. Good luck.
Try a terminal and type:
Anything muted in there? Using the right sound card? Click F6 to see what's available. I generally use Pulseaudio Volume Control to adjust sound which can be installed with:
sudo apt-get install pavucontrol