If the float of the fill valve (ballcock) is touching the tank you will need to adjust it to allow it free movement. There are fill valves that have no float. I fine these to be a great improvement over the float type ball cocks. When you say it won't flush, do you mean the water not go down or that by pushing the flush handle nothing happens. If the water will not go down than there is a block somewhere. If the flush handle does not lift the flapper high enough then it will have to be adjusted. More very good information is available in the links below.
http://www.fixatoilet.com/repair/waterruns.html
http://www.cidnetwork.com/Maintenance-toilet-problems.htm
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