The safe mode failure points to OS damage.
by R. Proffitt - 3/3/13 12:09 PM
In Reply to: Windows update went bad, now my PC is stuck in endless updat by edkron1
I rarely find safe mode to fail unless there are other issues such as malware or some overzealous protection software.
You didn't tell much but the usual fix given the slim details is to restore the OS from restore media and recover the user files from backups.
There are many safe modes. Command line, last known good boot, etc. If all fail, you should tell.