When I enable the gallery 2 module it loads blank, also I have this error code on the bottom of the page in the php debugging mode, not sure if it is the problem:

Notice [PHP]: Object of class XoopsUser could not be converted to int in file C:\Program Files\xampp\htdocs\xoops\class\theme.php line 442
Notice [PHP]: Only variable references should be returned by reference in file C:\Program Files\xampp\htdocs\xoops\kernel\blockinstance.php line 111

You don;t need to worry about php notices but warnings and errors are a concern. Please follow the read before you post instructions below as more infor will be needed. I am also chaning the placement of your post to module trouble shooting.
Cheers

I had same problem, refresh gallery module and system module.
It worked for me...