[v8volvo]

Does it start better if you jiggle the transmission gear selector around? If the park-neutral safety switch is going out that can sometimes be a sign. Or this can also be the sign of a dying starter that is ready for rebuild or replacement.

I've had a few different Volvos over the years (both gas and diesel) where I ended up having to add a standard style relay into the starter circuit. I think over a long enough time with enough wear and corrosion in all the contact points in the circuit (PNP switch, igntion switch, several connectors, many feet of wire) resulting in some voltage drop to the starter, when combined with an aging starter solenoid that may be getting a little weak, you can end up with a situation where the starter does not engage when you turn the key. Adding a relay in the circuit that is triggered by the starter signal wire to supply full clean battery voltage to the solenoid has been a reliable workaround for me. Although not the most elegant.

Smacking it with a piece of pipe can always work too, as noted, but if your issue gets severe enough that you are having to hit it with the pipe several times a day, then addressing it with a starter refresh and/or circuit diagnostics may have more appeal for you.