Hello,
It look really tight inside there, did the gpu actually touches the cpu block? If it didn't you are a really lucky vanilla in here.
Back to the point, you might have to upgrade your psu so you will be able to provide enough for 5770.
Edited: it appears that you haven't brought it. Be advised, the high performance video card has the really long board, completes with the shiny, decalized block that cover and ducts the air inside. You should check the measurement and determines if it will be able to fit in there.