I'm running Ubuntu 12.04, and my laptop* won't wake from sleep/suspend/hibernate. (Is sleep the same thing as suspend?) I'm not even sure which of these things it's doing. When I am done working for the day, I lock my screen (Control-Alt-L). When I come back the next day, the screen is in power saving mode, and no amount of typing or clicking (on the usb keyboard/mouse or the builtin keyboard/trackpad) nor tapping the power button will bring it back to life.

The only way I can get my machine to work is to hold down the power button until it shuts off, then press the power button again to turn it back on. Obviously, anything I had open from the previous day is pretty much gone -- in particular, my VMs all get rudely shut down without any warning.

This is driving me INSANE. I spend the first hour of every work day trying to figure out how to get my computer to stop locking up over night.

What I've tried:

1. Editing the org.freedesktop.upower.policy to disable suspend and hibernate.
2. Setting power management options in "Power" section of "System Settings".
3. Looking at all power management options in the BIOS (none appear to be relevant to sleep/suspend/hibernate).
4. Reading every forum post/askubuntu post that I can find that's even tangentially related to the subject.

My question: how to disable the automatic sleep and/or hibernate (and/or anything similar) in Ubuntu 12.04. I don't care if it's still possible to sleep/suspend/hibernate/whatever by pushing buttons or running some command or reciting led zeppelin lyrics backwards. I just want my laptop to be ready for work in the morning.

*The laptop is a Dell Latitude something or other. I don't want to get too specific because I've seen a lot of similar questions get closed for being too specific. I think my question is generic enough to stand -- it's a question about the latest, stable version of Ubuntu.