I should mention one thing that may help someone solve this problem:
After implementing the suggestions on the web, for example setting vga=795 in /boot/grub/menu.lst and updating the resolution in usplash.conf (and doing the associated rebuild), I see one change: when I shut down the computer, no longer do I see just a blank screen immediately (even before the computer has switched off), but now I see a screen with lots of random coloured 'noise' (lots of colours filling the entire screen).
I should mention one thing that may help someone solve this problem:
After implementing the suggestions on the web, for example setting vga=795 in /boot/grub/menu.lst and updating the resolution in usplash.conf (and doing the associated rebuild), I see one change: when I shut down the computer, no longer do I see just a blank screen immediately (even before the computer has switched off), but now I see a screen with lots of random coloured 'noise' (lots of colours filling the entire screen).