There are all kinds of potential causes for a symptom like that. You haven't provided much information to go on. Can you identify some of the programs this happens with (all or just certain ones)? Are these programs that reliably worked before and now sometimes don't? What happens when you double click on it (any activity or messages; does it look like it starts to load and never completes or there is no indication of any kind of response)? Does it affect your computer in any other way (just failure of that program to load or does other activity on the computer get affected--for example, everything becomes slow or other things become unresponsive)? Are there any other symptoms already occurring at the time these programs are unresponsive? Have you made any changes to your computer recently (new hardware or software)? Have you attempted any kind of diagnostics or general purpose "fixes" (if so, what and what were the results)? Does this happen mainly right after booting up or long after?
Just to throw out one common cause, there are times when a computer is busy, like when you first turn it on (there can still be stuff happening in the background at the point the computer looks like it's ready to use), or when you quit another program (there is often "housekeeping" when a program exits), or when you load another large or complex program, like a browser and then click on a second program while that's loading. If you try to launch a program while the computer is busy, it will often take much longer than normal to load and it can look like it simply did not respond to your mouse click. If you just wait for it, it will eventually load normally. However, if it looks like nothing is happening and you try to launch the same program a second time, this will often cause both instances to fail. In that case, logging out would clear both from memory.
Without more information, there is no way to know if this is what you're experiencing, but it is a very common cause of the symptoms you described and it's easy to check out. If this isn't the problem, get back to the forum with more information and other potential causes can be explored.
