Have you seen that sometimes one of yours many programs starts "Not Responding": Such a scenario can happen many times, some examples I know of are:
1. When shockwave flash in Google Chrome stops working
2. When you load too many programs.
What generally happens when you load a Program is, you try to bring its content from RAM(Random Access Memory)/ROM (Read-only Memory) to your cache, so that it will easily loadable or re-loadable.
When you load a program to your cache, you are trying to change a virtual physical address that you obtained from the RAM/ROM to a physical address of the cache. Now the programs that are already existing in your desktop have taken the physical address of the cache, when the newly loaded program tries to replace the physical address of the already existing program, a conflict occurs, so there is a temporary pause in the progress of the program (the state of "Not Responding") which is soon recovered by the processor and you get back your working program.
Note: Information piece of information I gathered, any queries/feedback are appreciated.