Thank you. I want to help, but before I can, I need to know what species the tree is. Many different kinds of trees are used in bonsai, and care is very different for each type.
Is it an evergreen with needles, or a deciduous tree with leaves?
Is the whole plant turning brown, or only in certain areas?
Is it possible for you to post a photo? If so, you can upload a photo by clicking on REPLY, then at the top of the area where you would type is a tool bar with icons. Click on the little paper clip icon (it's right next to the YouTube icon). Instructions will pop up. On some browsers, this doesn't work. if that happens, you can put your photo on one of the free photo sharing websites, such as www.photobucket.com
. Then come back here and paste the link to your picture in a REPLY.
If you can't provide a photo, describe the tree to em as best you can, and we'll go from there.