According to your title, you are getting an error, but according to the last statements, you are getting nothing on the page... Which is it?
Now, I will tell you this. You have major issues with your opening and closing php tags. <? ?>. You never close your initial php tag when you start throwing in regular HTML. Then you start throwing in unescaped double-quotes, which will cause your code to fail, and (more than likely) not display anything. Then later on, while your PHP tag is still open, you open another php tag.
Hopefully, by what I have described, you will get the idea, and will know how to fix it... (Hint, after your mysql_select_db statement, close your PHP tag. Then at the end of the code, remove your closing php tag.)
Also, I recommend you avoid using the short tag notations in your input values ( <?= )
Instead, get into the habit of using ( <?php ). This way, your code will be able to be portable across platforms. Some webhosts have short tags disabled, and your code would fail on them.