Sonething has happened to my game files. I really need help

[Izzy_Fleming12]

So today I decided to go onto Stardew for the first time in maybe a month and it said Steam wasn't installed so I installed it. Everything was ok until I went to look at mod options and there were no mods. I thought I was playing on my original game files but I wasn't so I went to look at the files and it doesn't look anywhere near the same as my old ones. I'm so confused, I can't even add my old mods back to it. I don't know what to do, and to be honest this is stressing me out so bad I nearly cried :p
PLEASE any sort of help at all is extremely appreciated!
Thanks :D