Q: camera not working

m using mac book pro retina early 2015....after i upgrade my mac to sierra..perviously i was using yosimite...after upgrade my camera stopped working...it show "there is no connected camera"...this problem started only after upgrade...how can i fix this problem...aslo my font is lost....instead oof other text except english it shows ???? symbols...my prexisting wallpapers are also lost...and