I've been experiencing a problem recently with my Linux laptop, where the display is blacking out during boot. I won't go into the specific details, as I have asked a question about it on Unix & Linux SE here.
The behavior during boot seems rather inconsistent. Sometimes the display blacks out early in the boot process; sometimes it gets to the graphical login window and then blacks out when I log in.
So, what I'm wondering is: in general, does inconsistent behavior of a computer always indicate a hardware issue? My thinking is that seems logical, because code should be static, unless the filesystem is progressively becoming corrupted (which would point to a failure of the hard disk in any case). So, any inconsistent behavior must then point to an underlying hardware issue.
Is that correct? Are there any situations where a software issue could cause inconsistent behavior?