Starting a Volvo involves a mechanical lock and an electrical switch, and each can develop issues after years of service. You must diagnose and service them separately.
Loss of oil pressure for any reason is the first smell of death. Most equate loss of oil pressure to low oil level, a common cause of low pressure in the history of the ICE.
Electrical consumers working in unison to properly function can put quite a load on the vehicle’s electrical system, which at times can struggle to keep up with the demand.