There is a reason why people aren't volunteering. Once that reason is discovered (if possible) that will be a key to resolving the issue.
I know for us we have experienced that in the past and have done several things to try and resolve the issue.
At the end of last year we sent home a form that basically asked what parents WERE willing to volunteer for. The person who created it told me she got it from the File Exchange program here but I haven't found it yet. Due to that I have uploaded the survey
here
. In our cover letter it basically said that we wanted to know what people were interested in so we could plan accordingly. We would only hold events that people showed a "passion" in participating in. Perhaps your cover letter needs to be a bit more "tough love" and let the parents know that without volunteers stepping forward to do events they can (and will) be canceled. I am not normally an advocate for canceling events as I think it gives off a very negative impression. However, sometimes the reality of a situation is necessary to achieve a response.
It may be that too much is being done, people just can't afford it, or that they aren't sharing in the same "passions" and events at your school need to be changed/revised/etc. Change is never easy but it may be necessary.
We also started the
2 Hour Power Pledge
this year, which has been very successful.
And as one last thought.... just because you are President doesn't mean you have to take everything on. I have been there done that so to speak, it is very tiring not only on me but my family as well. You have to be the one to set boundaries and stick to them, no matter who complains about something not happening. It has been amazing that when it was basically said that some things wouldn't happen without people to lead them, and then my stepping back COMPLETELY, and offering direction/advice only from a distance, how many more people have come forward. We actually have 2 events this year that are being planned by volunteers NOT on our board. This is a first for us.
Also, when someone brings an idea my standard response is "That sounds like a great/interesting/possible idea. Feel free to work something up about it for board approval and let me know what dates might work for you to take it on." Amazing how many "great ideas" get left on the table... In my mind though if they were that "great" though someone would have a passion about them and would want to head them up. Trust me, it isn't easy, I still have to check myself frequently, but it is necessary.
A few years ago the president before me made the comment that "PTO President" meant "honorary gofer" and nothing more. I refuse to function under that concept.... perhaps you need to make that same decision.