Another suspect is the block temperature sensor located near the camshaft cover at the "back" of the engine beside the firewall. The 960 has two temperature sensors-one at the "front" near the thermostat for the drivers gauge and the second for the computer.
I had similar symptoms to yours and replacement of the computer sensor solved the problem.
Replaced by my local indepedent mechanic.

Since your '95 has the built-in fault code reader see the FAQ's to see how to read your codes the next time it happens. (Maybe there is a code already stored, like 2-1-4, RPM sensor signal intermittent)

A possible part, that might become heat sensitive as it starts to fail, is the RPM sensor, located at the back of the engine in a bracket at the bell housing joint. If it is that, an error code should be set, 1-3-1.
--
'96 965 with 16' wheels at 102K. Had '85 745 Turbo Diesel for 200K.

As John states if it does not crank than it is most likely is the switch, if it cranks but will not fire up, then I would check the fuel pressure regulator. Disconnect the vacuum line and see if fuel is in the line. This happened to me, where the regulator died and was allowing fuel to be sucked into the manifold when the engine was warm, this cause a very rich condition which flooded the engine and causing hard if not impossible starts.

DanR 94 964 221,000 miles
--
DanR

It would be important to know exactly how it's not starting. Does it turn over and not catch or is there no activity when the ignition is turned? If it's the latter, your problem may be the infamous PNP switch located on the transmission. This is a classic sign of one going south. Also check to see whether your back-up lights work. I know that sounds looney, but its a looney piece of equipment.

If these are the sypmtoms, you're due for a new switch. In the meantime, sometimes rapidly operating the shifter back and forth (6-8 times) will help clean off any crude that is causing a poor contact. Otherwise just sitting to let it cool does seem to help.
--
John Shatzer, '97 V90 @ 94K