Q: Oil light is on

There are a variety of possibilities that could be at play here. The oil light may have come on due to low oil pressure which may be what has caused the rattling you hear. If this is the case, there may have been some engine damage done due to the lack of oil and proper lubrication. This will need to be inspected to determine what specifically may have caused this to happen.

The issue of the car not starting may or may not be related to the potential damage caused by the lack of oil as there are many different reasons that may cause the car not to start. This may be related to many different possibilities, some of which may be related to a lack of spark and some of which may be related to a fuel delivery problem or a combination of both. For example, if the ignition coils, crankshaft position sensor, spark plugs, spark plug wires or ignition module are faulty, this may cause the motor to not produce the spark needed to ignite the fuel in the motor. In the case of a fuel delivery problem, this may be related to low fuel pressure, faulty or dirty fuel injectors, a faulty or dirty idle air control valve (this relays information about air intake to the computer which makes fuel adjustments), or potentially a faulty fuel pressure regulator or fuel pump. Fuel delivery problems will typically not allow the proper amount of fuel to be delivered to the cylinders which results in a lean fuel condition which can cause backfiring or simply cause the motor not to start as a result of fuel starvation. I would recommend having an expert from YourMechanic come to your location to diagnose your no start problem.