I have emptied a few tanks with small leaks. It is worth it to check all connections like regulator to tank connections, regulator to hose, hose to disconnect, disconnect to keg post, keg post to keg, lid seal on keg. These are basic connections and list grows if you have a larger setup.
The tank obviously worked for a few days since you were pouring from it. Freezing makes things contract so maybe that's when it gave out. I would get it filled, get the fridge to the correct temp and check for leaks. Use a soapy water mix and spray connections listed above. If it starts to form bubbles then there is a leak and address that part but still check all of them incase there are multiples.