'About this Mac' will not work anymore
is there anything specific you can tell us about this problem?
For example, when you click 'about this mac' does the tab flash, confirming that you have in fact clicked it? and if so are you merely receiving a "rainbow spinning wheel of death" issue?

Either way, I have done some research into this and it appears that you are not alone in this problem. Most people have suggested simply bypassing the problem by launching the "System Information" application found under the "Utilities" folder inside "Applications", which will give you a far more in-depth insight into your mac than the "about this mac" tab ever will. However this is an unusual problem which should not be placated simply by bypassing it.

To solve this problem  i would suggest a few things, firstly: what was the last thing that you did before this error appeared, it could involve installing something odd or an unusual system crash (which may not have been your fault). If it was something unusual than it may be related to the error and could solve it through its reversal (if at all possible).

The second is to try and repair your disk permissions, by entering the Disk Utility application (Applications/Utilities folder again), and clicking verify and finally repair, which may well solve the problem. After this, i suggest a complete restart of the computer.
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Suggestion source: https://discussions.apple.com/thread/2686259


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If worse comes to worst, you can always completely reset the machine, however this is somewhat overkill for such a minor issue.

Hope that this helps.