Welcome! Although it would be more helpful to create a new thread for your isolated problem, let's see...
Accordingly to Cafe SDK (don't ask where did I got it) a blinking blue LED means a bootloader/software failure, or some weird times an APU issue. There's some other reasons for this, e.g: a dirty fan that doesn't flow air correctly, some kind of electric failure that fried some component, even a HDCP issue (according to the Internet the Wii U has HDCP standard... that's new), overheating... there's a lot of 'cause for this, and most of them as overheating, electric failure or a failing fan relate to the APU issue.
Firstly, I would suggest to check the HDCP option by unplugin the HDMI from the TV and the console, then turnin' off completely the Wii U and the TV (even better, unplug 'em from the outlet), pluggin' in the HDMI and then trying a power cycle.
If that doesn't work, try to change the thermal paste, and verifying that the fan is working properly.
In the case any of those tips work... well, maybe someone could lead you to the right direction, but that's the only "easy" solutions I know. The final step I would do it that case, would be to replace the motherboard, in which case would be the same as buying a new console.