Hibernation/ Suspend - I'm in the dark

[tpprynn]

I don't think I've ever properly understood Hibernation and Suspend or Sleep functions in general, whether in Windows or Linux. Could someone here summarise things in relation to Mint (13, Cinnamon, 64 bit)?

I was sure that up till a few days ago the computer would go into a sleep mode, or whatever is the correct term, if I didn't use it for some time - but it would run again if I pressed a key. It would wake up. Now I have to press the button on the front to leave sleep mode. Or is there a difference in what's happening? That is, when I could wake the pc up with akeybaord key, was that in a different mode than when I have to press the front power button?

I've recently moved my computer stuff about so that it's now sat on the floor so I'm not too pleased, with my back condition, to have to bend down. Can I get the key trigger back?

(I'm using a self-built AsRock-based desktop computer with the number 68 in the motherboard's model name - sorry - with an ATI HD 5670 graphics card, 128gb Samsung SSD, 3.1 ghz AMD dual core cpu - X2 240 something or other, and 4gb RAM. At one point I did enable an ACPI setting in the BIOS but that was possibly a week before the recent change in the computer's behaviour. I also have Mint 13 32 bit on an IBM Thinkpad X60s and 32 bit Mate edition on a Thinkpad T22, though I'm not so fussed about mastering this issue with the T22.)

[veggen]

This is a simplified explanation (I don't know exact details either), but should be enough:

Sleep/Suspend/Stand by = Most of the stuff is turned off, but RAM and other necessary equipment still gets power to retain what you have running. Some computers will remain visibly turned on, some will appear as if they're off and require you to press the power button, but unplugging them from the wall while they're in sleep would still lose you data.
Hibernate = Contents of RAM are serialized to disk and the computer is actually turned completely off. When you turn it back on, it detects the serialized stuff and uses it to reinitializes itself to the same state. Unplugging the hibernating computer loses nothing, as the computer is off anyway.

Not sure what is happening to you though. Maybe you unwittingly started using a different mode, or maybe you changed some hardware and now you're getting different behavior.