If they were on the iPad when you last synced/backed up to your computer's iTunes then they should be in that backup, so if you restore the iPad to that backup you should get them back on the iPad. You will need to restore the whole iPad, you can't restore individual apps or files, and you probably won't be able to use/extract content from the backup without restoring - I don't think that it is in a user-readble format on your computer. On Windows 7 I think that the location of the backup is here :
Have you not got copies of your presentations/content outside of the app e.g. already on your computer, external drives, cloud storage etc ?
Tank you King, very much!
Everything worked well.
I found a backupfile in my server and therefore was able to reinstalled everything.
You asked me If I have made any copies on my PC of the presentations.
My presentations are everyone very big (between 140-460 pages - full with pictures and texts).
Therefore It´s not possible to send them via e-mail.
Beacause I only use a PC (not an Apple) to my iTunes/iPad I have no posibilities to send and save my Keynote presentations in another medium/tool (iWork, iDisk, WebDAV) - please correct me If I´m wrong?