If we were talking about the importance of energy and that even machines need it what should we say?

What's the difference between these two sentences:


  Machines wouldn't work without energy &amp;
  
  Machines won't work without energy


and between:


  Machines couldn't work without energy &amp;
  
  Machines can't work without energy



Question: IE9 RC crashes on my Windows 7 laptop?
Answer: Does this occur on pages with flash or any other plugins?
Have you tried checking memory in your computer?  

I can't really have any other idea. Other apps misbehave too? (To be honest I don't really have an idea why would you want to use IE9RC if the other apps work like a charm. Like.. it only have GPU accel.. like Chrome and Firefox's latest beta. Nothing new, nothing special.)