Lost photos

After synching my iPad to my PC my photos disappeared. Can I retrieve them, and how do I prevent this happening again.. Tks

Did you copy the photos to your PC with the windows utility that pops up when you connect it to the PC? There's a check box that you can decide to erase the files from your iPad when it is done copying the pictures. The pictures could still be in your My Documents folder.
While your iPad is connected to your computer look in iTunes at your device. On the general tab there is a diagram that shows how much the files on the iPad take up. It is color coded and you can see if the pictures are still there.
Another place to look on the iPad is in the photos app under the photo stream folder. There are pictures in there that I had deleted long ago. I thin they are still taking up room.