[JLPrairie]

Both c and a. The layer of food you found is called a hoard, a for new hamsters for their hoard to be removed is very stressful. It's similar to coming home and finding that your fridge and freezer are both completely bare.
Remove the soiled food and most of the feces (keep in mode that hamsters do eat their feces) and put the food back.
How often are you feeding Hammy? Feeding whenever the bowl is empty is a poor way of feeding. 5-10 grams of a good nutritious mix (ca you tell us what mix you are using?) and a little sliver of fresh fruit/veg every day should be okay. Supplement daily with some source of safe animal protein (when in doubt, ask!) and fiber every two days. (Note:these are my personal ideas.)