Timeline entirely filled with red

Hey guys,

Recently bought a refurbished iMac from Apple. 2017, 4.2 GHz, 16gb of memory.

Installed Final Cut Pro and started editing away! No plugins or anything. My media is stored locally. The timeline then filled with red, following no specific action on my behalf. I rebooted and reinstalled FCPX, but to no avail. Even new project timelines are filled with red.
Any ideas?