If it is plugged, you may be able to clean it out.
That is assuming, the water has not gone down to far for your well.
You can use compressed air to blow the well out.
Run a 1/2" pipe down to the bottom of the well, and use a compressor to blow the water out. Do this 10 to 20 times. You may be able to see if the water flow improves or not. If the water has dropped lower than you well point, it may not do any good.
There is a product called (new-well). It is used to rehabilitate old wells. Sometimes it works, sometimes it doesn't. You would need to talk to a well supply house to it's proper use. It is a type of acid, and caution should be used.
As for going deeper. The sand that your well is set in, may not go any deeper than it is now.
You should check the depth of your well, and compare it to other close by.
If others are 15' to 25', and yours is 25'. Chances are not in your favor that going deeper will do any good at all.
Just some thoughts I had.
Hope it help some.
Travis