My wii u console has a blinking blue light

Blod... blue light of death!?

Could try leaving it online over-nigh,see if it finishes updating... but most likley a hardware error/failed update... need to call nintendo helpline! Clean fan/vents with small paint brush if dusty! and dust it before you send it. If you have a receipt and it's less than a year old it may be a free fix! if not then Cost is £54 unless they find user damage then its £175 !!!!...But will be free post at least. They text you on progress and let you know.

My one was blinking light only at power on, no disk sounds or conecting to controller...cost £54 due to hardware fault...the console had never been opend.