Hello, I have recently bought a 2000 Volvo S80 and I’m stumped on how to fix it. It is not starting, it is not cranking, just a chime when you put the keys in an I’ve tried several method to crank it. It is showing (Start Prevented, Try Again). The car has 135k miles and only 1 key without a fob.

All the things I’ve checked and tried:
Checked Battery at Auto Part (Reading 856 CCA/900, 12.55 Volt)
Checked Starter at O’REILLYS (Cranked & Started 3 times)
Checked All Fuses & Relays (no sign of anything blown)
Checked it with a OBD2 Scanner nothing shows up
Tried to clean the terminals of the starters & battery
Tried the unlocking & locking the car 5x
Tried unplugging the ECU fuses from dash & the engine for 5 mins.
Tried connecting the positive & negative terminals of battery and leaving it overnight.
Tried to the odometer reset by holding the odometer mileage & putting the key In Acc. I and then turn it into II and holding it on there for 10 seconds and turn it off.
Tried jumping the starter with a screwdriver and manage to crank but would not turn over.

I drove the car before this happened back & forth to work. It did have a coolant leak from the reservoir but I fixed it and when I try to crank it in the morning for work it would not do anything.

if anyone have any idea what this could be it would be great. The nearest volvo dealership is about 100 miles and it wouldn’t be worth it if I get it towed there.

 

12.5 volts seems a bit weak, you want 12.7. I would first jump it of a good battery or a charger with a "Starting" position.
That said, whenever I work on a running car and it won't start afterwards (it happens) I go over every single thing I touched, every area that I may have left a vacuum line unattached, every electrical connector, etc. If it isn't the battery, you'll find it,

As an example from real life, last summer I replaced my air filter, a few days later the battery (fairly new) was dead. eventually I found that I had jostled the vacuum pump control valve, cracking it. The pump just kept running until the battery died.

Some things I saw in your post - I have seen all sorts of voodoo fixes on cars - "Unlock drivers door 3 times while standing on left foot and singing Inna Gadda De Vida," sort of stuff. The internet is rife with them. They don't work. if it doesn't make sense, don't waste your time.,

 

I have checked every little thing in the engine bay to see if I left something unhook or something is out of place. I tried jump starting it from another car and it doesn’t do anything. I hook the battery to a battery charger overnight and put it back on still nothing. I had a mechanic come and check it out the other day he said it’s either your ignition switch or your key. Because the car will crank when he jumped the starter. It was just not allowing it to turn over.

I researched some more that by turning the key to the Pos. III and tapping it firmly with screwdriver handle it might start up. I did that and no luck. Then I noticed that the antenna ring is not lighting up. So that’s probably what I’m going to replace and go from there.

 

imobiliser which sits around the key is worth changing. Get one from a breaker's yard and see if it works.

 

I forgot to mention banging on sensitive electronic components.
I think you would be money ahead if you stopped looking for "fixes" youtube and have the car towed to a mechcanic,