Engine light and heaters not working why?

What trouble codes are you getting?
Check the coolant level.

How much do you understand about cars?

If you do not have coolant or or insuffcient, it would definitely overheat.
Trouble codes means what the scan tool registers, not the description. Exact trouble codes are required.

You need to check where the coolant is leaking from. The overheating is the source of the problem so you can forget about the injectors temporarily till the coolant leakage is resolved.

There is no necessity to strip the engine to do that, unless the head gaskets has been damaged due to the overheating. A pressure test should be able to help you determine the source of the leak. If you had been using coolant in system, they would leave a noticeable trace. Most common leakage areas are hose joints, water pump, radiator cap, heater core and radiator itself.

Remove whatever cover you have over the engine and fill up the cooling system. Try not to spill anything into the engine so that whatever leak that is present would show correctly. Check for leaks and if none fould, start engine for 5 minutes. Do not close the radiator cap yet, top up whatever coolant necessary to fill the recovery tank to the correct level. If coolant level stabilises, close radiator, if not and coolant seems to overheat, stop engine and wait 5 minutes. Restart engine and top up coolant. Close radiator cap and check for leakages. There would be pressure in system after 1 or 2 minutes. Stop engine after 5 minutes and check for leakages. If you do not see any leaks, you would need a pressure or chemical to determine if the head gasket is bad.

No sound when turning the ignition key is not a bad head gasket.

The battery, ignition switch, starter and security system are list of things you should be looking at.

A head gasket job is not too cheap but prices varies so you should be checking locally for an accurate assessment. It can range from 800 to more thaan 2 k depending on what needs to be replaced.