Turn on
If you've disassembled it before, maybe the problem is the ribbon cable. If you've never pulled down your console, maybe a fuse in the power supply is blown. If you've never opened the console before, get support to fix it. If you have, then try and find if you didn't reconnect something, or test and see if the power supply is working ok. Hope the info helps.
PeAcE.
PeAcE.