What operating system are you using?
Have you ensured you have the latest version of Quicktime, per the program's requirements?
Note that version 8 is a relatively old version, in terms of video technology. (Do make sure you've got the 8.01 update.) It's designed to pretty much work with miniDV, HDV and DVD video. Support for AVCHD and MP4s is very primitive in version 8 and gets much better in later versions of the program (especially after version 11.)
Adding Quicktime to your system may improve its ability to work with MP4s. But if this video is coming from a phone or other non-camcorder source, version 8 just may not do it well or even at all.
I'm using win 7, Quicktime is up-to-date but i don't have 8.01 and my video is recorded by bandicam in mpeg-4
You need to make the Bandicam file compatible with Elements.
Convert with HandBrake to constant framerate then import into PE.
Next time when using Bandicam use a different codec (one that PE likes) to record.
Exellent, it all falls into place...