Starting a while back, I was having what appears to be the same thing happening on my main system which is an AMD Phenom quad core 3.4 Ghz processor and running 4 Gb of memory. This is the 32 bit pclos kde OS that I have been running and updating almost daily for years.
It was happening a couple times a day with other symptoms besides the total hang.
Sorry at the moment I don't remember what they were.
Anyway, I was running the 3.2.18-pclos2.pae.bfs kernel when this started.
After a couple days of this, I thought to boot using the previous kernel which is 18.104.22.168-pclos1.pae.bfs.
I have been running on the 2.6.... kernel for about a week now with no hang.
If you want to try booting with this kernel, I can reboot my system into the 3.2....kernel and see if my problem returns.
By the way, I am running an ASUS M4A89GTD PRO/USB3 motherboard and an AMD Phenom II 965 black processor.
Ok, I am back up on the 3.2.18-pclos2.pae.bfs kernel.
I'll report any hangs here if they happen.
I did get an odd boot already. When the kde desktop came up, I got a message to the effect that the Plasma Desktop Shell closed unexpectedly. When I closed that window, the screen went totally black except for a very small quarter inch by half inch window showing on the upper left of the screen. Dragging the corner of it to make it larger, produced a window having to do with "volume" but I don't remember what else it said because I have almost no short term memory and used the last of the memory on my digital camera that I use to document unexpected output on the first message about the Plasma Desktop Shell.
When I closed that window the screen went totally black so I did a Ctrl-alt-bkspace and got the normal log in window from which I was able to log in normally.
I suspect that this was just the result of being the first boot using a different kernel but I really do not know.
Well, it has been several days and my machine no longer has the problem no matter which kernel I use.
There have been a batch of updates since I first had the problem so I assume one of them must have fixed it.