2006 Nissan Altima was parked for 5 months and was now super hard to i

There are several possibilities, you can try. I would start by checking all the fluids and the battery condition. When I say fluids, I mean everything -- engine, transmission, brakes, coolant, and rear end. If any of the fluids seem abnormally low or thickened, consider topping off or replacing, and change your filters. Keep reading below and I'll leave that decision to your good judgment.

If you've already cranked or even started the engine, the next step I'm considering can probably be skipped. What I'm thinking about is the piston cylinders may have developed a very thin film of rust on the inside surfaces. Normally running the engine every so often keeps this cleaned off and all surfaces get a fresh coating of oil throughout the engine. What I would consider doing is pulling the plugs and hand-crank the engine with a big wrench. This step is NOT intended to actually jump start the engine, and don't do this if you've never seen it done before. And certainly don't do any hand cranking if the engine is in a state that it could fire up and try to run.

If you were already able to get it running, but it is running poorly, consider replacing the all the fuel. Regular gasoline can degrade in 3 to 6 months, ethanol-based fuels can lose its combustibility in 1 to 3 months, and diesel can last up to a year. Finally, consider taking it to a repair shop you trust. In fact, a professional once-over is advisable even if you do get it running.

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When I was in the US Navy, some of us would have to put our vehicles in to storage for 6 to 12 months or even longer while overseas. And if you need to do this again, you can see in the list below, that the process is very involved:

• Clean the engine of dirt and debris.
• Run engine so the oil is hot; stop and immediately drain and install clean oil filters.
• Use preservative oils on the engine by: removing rocker arm covers and gear train covers, spray these with a preservation oil.
• For gas engines, take out the spark plugs and spray preservation oil in each cylinder then spray each spark plug and reinstall.
• Loosen the the tension on belts somewhat to prevent fatigue and deterioration.
• Remove fuel from filters and drain the fuel injection pump.
• Grease linkages, rod threads, joints, and so on.
• Remove batteries and store indoors on wood blocks (not concrete floors) and put on a low-level trickle charger.
• Close off all the intake, and exhaust ports, as well as any other openings. Sometimes wasps and other vermin can take up residence.
• Place a waterproof cover over the everything.

To put back into service: a full inspection of the electrical components is needed. All preservation oils must be removed and refilled with manufacturer approved oil. Coolant should be tested and refilled, if necessary. And finally check tire pressures before attempting to drive.

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Alternatively, a number of people I know, would ask a friend or relative relative to babysit the vehicle by starting it about once per month to fully warm it up, and even drive it around for a day or two. I'm doing this sort of thing now for a relative spending a year and a half working in Mexico. This sort of thing is what I called "pickling the engine".

Best of luck with this, Doug