Is it possible that no water running to one toilet could be from frozen pipes?
It could very well be a frozen pipe, it could also be that the valve has become clogged somehow.

The only way to tell for sure if its a frozen pipe is either find the frozen pipe, or wait for it to thaw. If water starts flowing when the temperature warms up then you know it was frozen.  

If you have copper pipes, the worst case would be that when it thaws you discover a leak from a burst pipe. With this in mind, it is probably worth opening up the wall to find out for sure - way easier to replace a cleanly cut section of drywall then it is to fix extensive water damage.  Once you find the section you need to determine why it froze - is there no insulation in there? Can you remedy that?