Mac OS X Yosemite boot hangs out at 50%

Hi,

I've googled this bug and there are some Yosemite users with the same problem but I still can't fix it.

Last night I changed my macintosh HD disk permission that everyone could write and read it and since then when I want to power on my mac the boot hangs out at 50%,

-The Safe mode wont run either + I've tried the verbose mode too and it shows this line:

Bug in process suhelperd[178] : over-released legacy external boost assertion (1 total, 1 external, 0 legacy external)

Anyone with a solution?

P.s : Sorry for the bad grammar