Try the bucket of water trick down the toilet; if it flushes manually, then it isolates the problem to the operation of the toilet.
If not, it is either a clogged drain or the latter, lack of a vent.
Use a closet auger first, if that doesn’t cure the problem then pull the toilet and attempt to remove clog in this fashion.
“Your best interest is secured by making the right decisions the first time.”
» This message has been edited by DUNBAR on 06 July 2004