Which format are the source files your are trying to use?
One was a .pdf file and one was either an .mp4 or an .avi.
.mp4 or an .avi.
No deal. Due to licensing limitations, he trial does not include anything that would allow it to work with MPEG-derivatives. Those features are only available in the commercial version. Likewise, AE does not work with many MPEG-based variations such as DivX or Xvid wrapeed in AVI containers. For the trial, the only way to work with MPEG-4/ H.264 is to use Quicktime with these respective CoDecs used inside the MOV file.
What sort of PDF? If it is a protected/encrypted PDF, AE may not be able to handle it at all.
As for the rest - what exactly have you tried so far? Trashed the prefs? Cleaned out the Media Cache? Re-installs by themselves usually fix nothing, as they don't reset configuration data. Also, have you let the Adobe Updater run at first to bring your trial up to the latest?