Put the summary of the bug you're having here

What I expected to happen was...:
I expected my single player survival world to load correctly.

What actually happened was...:
I can play a world for weeks but eventually when I try to mine a block, chop a tree, or do some other mundane task the world freezes, the block continually breaks apart then reappears. If I try to reload the world it will get stuck on the loading world building terrain screen, if it manages to load the world half the chunks are missing. Also it will inevitably cause my computer to power down. I would like to emphasize that the evidence suggests that this is not a hardware problem. I have a new battery that is fully charged and it was plugged in anyway. The processor does not feel warm. The fan is functioning. I ran a stress test on my system and the processor (pentium core i5) didn't get above 55C (the online specs say it can perform at up to 105C). This does not happen when I run other games with similar resource usage (eg civilization). It only happens with Minecraft.

Steps to Reproduce:
1. Start a single player survival world on my system.
2. Play for a week or two.
3. Try to mine a block and it won't mine properly, repeatedly reappearing, and not dropping anything.
4. Try to load the world after this happens, it will not load, freezing on the loading world, building terrain screen or boot me back to the title screen, and then usually the computer shuts down.
5. This repeats every time I try to reload the world.
6. Uninstalling and reinstalling the game does not fix it.
7. Uninstalling and reinstalling Java does not fix it.
8. Following the "fix a corrupted world" strategy does not fix it.
9. Loading a backed up save file does not fix it.
10. New single player worlds will load and run for awhile but eventually corrupt too.