A little more context to your problem would be helpful. In general, the answer is 'no'.
Remotely shutting down any random computer is not usually a good thing to be able to do, so most are set up to protect from that happening. If sshd access is blocked, either by being disabled or firewalled, then that computer is even more protected, as it should be, and having root won't do you any good unless you're standing in front of that computer.
On the other hand, there are some compute centers that use management systems to do just what you're thinking. These are often supported either by a special daemon running on the computer, listening on a different network port than sshd, or by using low-level firmware utilities built into the network card. These scenarios require a little planning and won't help you if you've suddenly got a problem now.
Depending upon the age of the computer and the OS, there may be known attack vectors that might get you root access using cracking software. I don't recommend this route, but it exists.
One last idea - there are remotely operated power strips that could be used. If you know which computer it is and which power strip and which plug it is plugged into, you could simply turn off power to that plug. Again, this requires some preplanning, and you want to make sure someone hasn't plug their ventilator into that outlet.