Carpentry and Woodworking - Sander slips pads

I'm trying to sand some bookshelves with a craftsman 1/3 sheet pad sander (model 315.116112) that I borrowed from my father in law. The problem is as soon as I touch the sander to the surface I'm trying to sand, the pad flies halfway off the tool. It doesn't really seem to be sanding anything. Any ideas?

I have a DeWalt random orbital that I'm using to finish just about everywhere else that works great...I'm only using this to try to get into the corners (the DeWalt has round pads...the craftsman's are square). Is there an easier way to do that? Any help or advice would be appreciated.
Justin

Here is an Owners Manual:

http://c.sears.com/assets/own/00911702e.pdf

Scroll down to the pages showing how to install the paper. Hope this helps.

I appreciate your help, but that isn't the exact sander that I have...the clamps on the sander I have are on the front and back and not on the sides like that. Plus the sander that I have doesn't have a vacuum or bag attachment.

How did you find the manual? I did a lot of searching for it and just came up with lots of links for places to buy sanders.

Cut you paper long enough to reach to the clamps on the front and back of your sander and use the clamps to secure the paper.

I found the manual on the Sears website. Hope this helps.