mac version is not capable with itunes

my mac book pro version is 10.6.8

when i sync my iphone to the mac book pro, it pumped a screen saying that i have to upgrade my itunes to 11.2

however, when i finished installing it, it required me to restart my computer

i try to restart, but it then stop turning it off, and stop to a screen

my computer cannot restart even shut down

what can i do? i cannot sync my iphone anymore?