Volvo: starting problem 1989 240 GL, s 240, simple tests

Question
my husband's 240 gl, automatic, 95,000mi has 3x in recent weeks failed to start. He cranks it nothing happens, waits about 1/2 hour and it kicks over. The 1st time this happened, it occured 2x in 1 day. He left it at a mechanic's shop for 5 days but they could not get the car to replicate the problem. everytime they turned it on, it started. It happened again today. any ideas in what direction he should point the mechanic

Answer
Two basic things to check next time the car fails to start.  Pull out a spark plug when cranking to see if a spark is getting to the engine.  Next, pull out an injector when the engine is cranking to see if it is actually squirting fuel.  Those simple tests can point you to either a fuel delivery or electrical issue, usually 95% of the problem.  As a side chance, I had a similar problem with my Volvo a while back, and discovered I was getting no spark at the plugs.  Turned out the bare electrical connections that plug into my coil had corroded enough to cause ocasional shorting.  You could check there if you see no spark.  Basic idea in the long run is to decide if it is fuel or electrical, then begin tracing the problem back until the issue is found.