I have a computer hooked up to my old CRT TV using the s-video connection and running Mythbuntu. I do not have a monitor attached (just the TV), but I can SSH into the computer from my laptop.

It was working fine prior to my upgrade from 12.04 to 12.10. Since the upgrade, when the computer boots, it brings me to the log-in screen, but the screen is flickering as if the refresh rate or resolution is incorrect. I can just barely make out that my username is displayed on the screen, but everything on the screen is scrolling across the screen so fast that it is unusable. If I switch to a virtual console (ctrl+alt+F1) or shut down GDM (or lightdm) the virtual console is also flickering in the same way, so the problem isn't related to X.

I'm pretty sure I need to change something in the grub configuration (/etc/default/grub?) to fix this, but I'm not quite sure what.

I've already increased the time-out so that the grub menu is visible. When the computer boots, I can see the POST messages fine, I can see the grub count-down and hit "esc". I can see the grub-menu and choose advanced options, and that all displays just fine. Once I choose to boot Ubuntu, it says "Loading, please wait..." then the screen goes blank for a few seconds, then starts flickering.

Video card is an NVIDIA Corporation NV34 [GeForce FX 5200] (rev a1) (reported from lspci).