Can't change resolution

[arist]

I just upgraded my HP Mini netbook from Raring to Saucy, using do-release-upgrade. The display resolution is 800x600, instead of the normal 1024x576. System Settings shows 800x600 as the only resolution available. The video chipset is 945GSE by Intel, and the driver is i915. xrandr says

Screen 0: minimum 800 x 600, current 800 x 600, maximum 800 x 600.

This machine has been through at least 5 iterations of Kubuntu, and this has never happened.

Any help greatly appreciated.

[arist]

I tried xrandr --newmode with the proper resolution, and here is the result when running xrandr again:

xrandr: Failed to get size of gamma for output default
Screen 0: minimum 800 x 600, current 800 x 600, maximum 800 x 600
default connected primary 800x600+0+0 0mm x 0mm
   800x600         0.0* 
  1024x576_60.00 (0x1cc)   46.5MHz
        h: width  1024 start 1064 end 1160 total 1296 skew    0 clock   35.9KHz
        v: height  576 start  579 end  584 total  599           clock   59.9Hz

When I try xrandr --addmode this is the result:

xrandr --addmode VGA1 1024_576_60.00
xrandr: Failed to get size of gamma for output default
xrandr: cannot find output "VGA1"

[arist]

After hours of research, I concluded that there is no solution to this problem. So I gave up and tried to do a fresh install of 13.10. The install failed. Trying to install Ubuntu server also failed (Failed to install busybox-intramfs), so I went back to Raring, and that install also failed. But when I rebooted the system came up, and the resolution is fine. So after installing the software that I used to have, I'm back where I started. I really want to get the netbook to work with KDEConnect, which requires Saucy, so I'll try again.

Edit:
Having nothing to lose, I installed Trusty alpha 2. As usual, the installer crashed at the end, but after shutting down and booting, everything seems to work. Resolution is fine (vertical is 600 rather than 576, but I can live with that).

[arist]

You mean wiping out my /home partition? Only as a last resort.

[arist]

I don't understand what you mean by "a full disk." Do you think there's not enough room on /? I've always had these partition sizes, on every past version of Kubuntu. / has 12G. Surely that should be enough.

[arist]

I did a new install, and the resolution was fine, until I did dist-upgrade. Now the resolution is back at 800x600. I suspect a video driver was removed in an upgrade. Do you know how to get the old driver back? It's i915. I have no clue.