If you do not see the upload form it can be one of two things. The most simple is that _DISABLEUPLOAD setting. If you have set this setting to TRUE the upload form will never be shown. Change it back to FALSE if you want to re-enable uploads.

The other reason can is that PHP does not have write permissions to the current directory. In that case File Thingie will hide the upload form rather than have you upload large files in vain. To give PHP write permissions login to your server and CHMOD the directory in question to 777.