Can you hear the steam pump attempt to pump water? With these aging machines it is relatively common for something along the lines to get clogged with scale/crud which will mean the pump attempts to pump but nothing is flowing. I recently had a similar problem and had to flush my steam system due to a clogged pump.
Otherwise you may be right, the switch may have died. If you attempt to check the switch i would strongly suggest taking the back and top of the machine off or else youre very restricted by space. Taking the top off can be a fairly intricate procedure so do some searching and find a guide first.
Others have had this problem before, so doing some searching should reveal some links like this one - http://coffeesnobs.com.au/YaBB.pl?num=1293074472
*edit - linky fixed