Daming Off

My last batch of seeds mostly did not sprout out of the soil after a strong germination. The two of the ten that made it through dampened off within a day. How can I tell if it was user error with environment or fungi in the soil? Should I toss all my soil that is sitting in the storage shed?

happened to me with soil, ended up with dead plant, lucky it was early stages, had a investation in fungus gnats ...

Try pre-germination before you sow to soil.
Don't touch your seeds use a tweezers. you have salts, and oils on your hands that can be transmitted to the seed.
Scuff your seeds. Sand Paper Box.
Use a cloning/Rooting solution. let your seeds fall to the bottom of the Cloning/Rooting Solution. 12-24 hours
Paper towel soak in your Cloning/Rooting Solution, wring it out good, just moist towel, Zip/Lock Bag, Warm/Dark Place like the water heater or covered on top the fridge.
12-48 hrs they should sprout. check them every 12hrs.

Sow to soil the germinated seeds.
Plant Shallow. You want to see the top of the seed coat flush with the soil.
Root Down, Use a tweezers, Water the soil before you sow your seed.