Hi and

to the forum!
The media seems to be the most concerning specially the roots. I haven't have had enough experience with oncidium type orchids but I highly recommend repotting your orchid in fresh new media immediately, bark chips will do but if you plan on potting in semi hydro, it's ok. Clean the roots up first; cutting off dead roots, and dead roots are like spongey, soft, feels hollow and dry roots that don't green up so it's important to soak the roots first in water. You can watch Missorchidgirl's video on youtube to properly on how to properly pot your orchid and her orchid in the video kinda looks like yours! Hope it recovers