After fiddling around a lot with Rhythmbox and Banshee one day, I had to xkill them and logout a few times, and I think I remember seeing some error message asking for the keyring. I entered my password and it went away. After that, I had not realised that whenever I hibernate, the computer pretends that it has gone into hibernation and it seems perfectly okay, until the next time I start. The computer then does not resume from hibernate, it instead starts as though it had been shut down and I lose all unsaved data.
I suspected an error in swap and tried reformatting the swap partition in GParted and turned it back on, to no avail. On the subsequent boots, the swap drive is no longer being recognised, and hence now I don't even see the hibernate option. Of the possible reasons given by Gparted, I think this ("The device entry /dev/sda7 is missing") is the relevant one. How do I set it right and re-enable hibernation? (Even the command
sudo pm-hibernate doesn't work now since the swap partition isn't recognised.)