It may be that when you pulled on the front derailleur to get the chain back on, it pulled too hard on the shifter cables, breaking them or changing the cable tension. Check if the cables running down your down tube are broken, too loose, or too tight. Try adjusting the left barrel adjuster on the down tube to see if it changes anything. Replacement shifter cables cost ~$3, and the bike shop can replace it for you for under $15 usually.
