I wish I had more detail about your problem because there are several interpretations. Some people do go in for what I call "pencil-sharpening" - the things children do rather than face homework. I have even known them tidy their rooms when revision calls! It is a common response to not fancying the important task or not feeling up to it.
If your head is not up to it, you have to face the fact that you are paying a big salary to an office assistant, and in an extreme case, do something about it.
Even not feeling motivated to do the more demanding tasks is quite serious, though that is character rather than ability.
But ask yourselves whether he or she really spend serious amounts of time on photocopying and other completely mechanical tasks, because I can see another possible interpretation of the heavy computer use.
Coming rather late to modern technology, I have only recently realised how very few people doing high-level strategic jobs today want or need secretarial support as such. They regard their personal computer as part of their thinking process and use a wide range of its capacities. With this proficiency it is even quicker to do their own letters than dictate them, quite apart from the more complex ways in which technology can support their strategic thinking.
But even if we assume that your head is a person of high ability and a wizard with the computer, not simply an overpaid clerk, you still presumably have the problem that there are important issues which should be on the agenda of the school while he or she is too busy being busy.
The least hazardous way to approach these may still be through the issue of overload and time use, and concerned questioning by your chair about whether the head could benefit from any more help with routine tasks or more delegation. That should open up the conversation in an unthreatening way. But whoever approaches him or her must be ready to suggest how the necessary discussion and sharing with the governing body could be eased.
It might, for instance, lead to the possibility that certain subjects could be assigned to an appropriate deputy or other senior colleague, working with the relevant committee. Or it might be that very specific issues could be explored informally by small working parties of governors, just gathering information and setting out possible approaches.
You must be careful not to give the head the impression that you are trying to usurp his or her leadership role, but properly handled it could lead to a feeling of relief that someone is concerned about the workload and willing to be constructive.
Finally, although I sympathise with your frustration, we must remember that the load of responsibility on heads now is colossal and there must be more than one who does not know where to start.
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