iTunes Synchronization iPad with iMac fails

Oh happy days when my iPad was automatically synchronized after I connected it to my iMac by cable. Two month ago it was no longer possible and I was requested to update iTunes. It turned out that my 10.5 iMac was not sufficient. So I now bought 10.6 and installed it full of hope I now could synchronize. But this does not happen. System tells me, my iPad is not connected though it is. If I try to connect via bluetooth, it says my iPad does not answer. If I try to send something from iPad to iTunes nothing happens. What is wrong?
It is so annoying when things which always worked, suddenly no longer do, forcing you to buy an upgrade, and if you do it still do not work. I would not buy a car with such a menace
Can somebody help?

Which iPad do you have and what version of iOS is it running? Also we're assuming you have Snow Leopard 10.6.8 installed on your Mac?

Keep running Software Update until it says you're all up to date, and specifically that iTunes is as well.

It all works with my wife's late 2007 24" iMac running OS X 10.6.8 and her iPad 3rd Gen.