there is a small metal clip when you open up the ipod touch 1st generation back panel its a little golden clip next to the ribbon that connects the digitizer here is a picture:
[image|80057|size=thumbnail]
If that Clip isn't there then thats your problem I recently had this problem I had used the metal piece from a pencil I cut it with scissors and folded it and placed it in its place and closed it up after that it worked fine.
Hope this is Helpful :)