Take a look:
I did a fresh install of Cubase 7 64 bits(in a refreshed windows 8 64 bits) then update it to 7.0.4.
First I recorded some tracks (without enter the mixer) then When I opened the mixer, the racks didn’t appear, now well as you saw, nothing appears!!!
I tried rebooting again, closing and open again cubase, connecting a second monitor and nothing.
If a open a new project, the mixer appear again, but well I have a big job coming up this monday, recording (non stop) during 8 hours, I can’t afford lost the mixer in the middle of the job
Ps: I don’t know if its important but the project is 3 hours long.