Car drove great one day but the next day it started overheating after driving about 5-7 minutes. Had the thermostat changed, the coolant reservoir and cap changed, coolant changed twice, hoses checked. Still overheated after driving 5-7 minutes. Different mechanic added a sealant to the coolant reservoir but still overheats. Heater does not blow hot air. Have put a lot of money into this car in the last six months so I need an answer that works. Please help!

The puddle is in fact frost and condensation from the AC system. It is normal that this happens and you notice it 5 to 10 minutes after you park..

Top up the coolant anyway.

You may have a blown engine head gasket. Check your oil to see if it is milky because water is getting into the oil, and check the water to see if oil is getting into the coolant.
If you have either of these, you may need to have a new head gasket for the engine, and hopefully you do not have a cracked engine head.
This will require a fair bit of work to fix correctly. Your local garage or mechanic may be your next call.
There are some products you can use in the coolant for either of these, but it is only a temporary fix.

sounds like the radiator is blocked either coolant flow or ext air flow through the matrix the thermostat can get ruined when the system overheats so allways change the stat after a overheat problem GET THE RAD CHECKED FIRST if ok check the coolant pump

First question is what constitutes "overheating".
Since the car has been parked for years, the thermostat could be sticking closed.
The cooling system could have air pockets and need to be bled.
The water pump may be corroded inside and not pumping enough volume.
If the gauge goes above half way, the fans should start up. But half way should be more or less normal, not hot yet.
I would look at flow problems first, beginning with removing the thermostat and driving it without one for a few days. Also check and see if there is a process to bleed the cooling system of air.

thats due to low or no coolant, you shouldnt drive this overheating engine damage will occur,the first thing is to fill the radiator up, and look around for any leaks, if no leaks are seen, then start engine and allow it to warm up, leave cap off at first to top off coolant, after a few minutes install cap and let it run, keep an eye on the temp gauge and also watch for leaks. this problem is due to a coolant leak,maybe a hose is bad or it was low on coolant or you have a bad thermostat, good day.

Subarus can be challenging to "burp" Sometimes it takes several attempts to get the air out of the system. The procedure is simple. Top off the radiator, squeeze the hose a few times to help get the air out, replace the cap and start the car. let it idle or drive slowly near home with the heat on high. once the temp gauge begins to rise, if there is no heat get the car back to the driveway before the temp gauge gets half way. Shut the engine off wait for it to cool, at least 10 minutes. Then check the radiator again. If there is still air top off again and repeat. After 3 or 4 attempts if there is still air and or the coolant reservoir seems to be filling, try replacing the radiator cap. If this doesn't solve the problem, It may be a head gasket.

A couple of possibilities. You should consider changing thermostat and coolant. Also fan belt that drives waterpump should be replaced, and lastly new radiator/coolant cap (they do loose ability to hold pressure)

Removal of the thermostat from the cooling system is not a good idea. This upsets the coolant flow rate in the system, and that can cause the engine to overheat, even when no other problem with the cooling system exists.

Try to identify the cause of the overheating.

Ensure that engine tune, or other engine mechanical fault condition is not the cause of the overheating, then go through the checklist following:-

1) Check engine cooling fan/s are operating as required when engine temp rises above cut-in threshold - check fan control relay is ok,
2) Check for collapsing radiator hose on suction side of water-pump when motor revs raised above idle.
3) Check coolant reservoir pressure cap is serviceable,
4) Check coolant system is properly filled - carry out any bleed off procedure specified to clear any air locks- (ensure heater core coolant flow is turned on).
5) Check for combustion gas bubbles in the coolant reservoir while the motor is running - this indicates a blown head gasket. If in doubt, take it to a radiator shop and ask for a combustion gas check on your radiator.
6) Check condition of radiator core:-
i) for blockage of air flow to (bugs/grass etc),
ii) for core internal blockage to coolant flow,

If all above ok, replace the thermostat again (also ensure it is not installed upside down) - faulty new thermostats are not unheard of.

Check for leaks around the Coolant Overflow Reservoir (the yellow bottle in the middle of the firewall.) I had the same problem with over-heating, and replaced the thermostat with no help. I went to the dealer and picked up the Reservoir for $26~, installed it in 5 mins (at work) and haven't had a cooling issue since.

looks like you have done everything but the problem with your car is that the cylider head gasket has gone have a look at the dipstick or remove the oil filler cap if it looks like mayo then 100% head gasket has failed you said no water on the floor so it must have gone into engine only way this can happen is head gasket failing, if you have put lot of water in to the cooling system then your sump will be full of oil water mix.

let us know your findings so we can help you more if you need it