Does anyone know hot to fix this? I think I lost all my coins! I can't find the folder with my old wallet data after installing the new wallet.

if you have backup .dat file, your coin is safe
open your task manager, do end task all digibyte.exe activity and try to open again, remember dont click digibyte core testnet
just click digibyte core (32/64bit)
I have tried to restart the wallet more than 10 times. I get the same error. I deleted it and re-installed it, still the same error. I need help!