Moving this discussion to the Premiere Elements forum.
What operating system are you using?
If Windows, have you manually gone to Windows Update and ensured you have the non-critical updates (which dont' download automatically)?
How fast is your processor, how much RAM do you have and how much free, clean, defragmented space is on your hard drive?
Welcome to the forum.
Along with Steve's comments and questions, what version of Apple's QT Player do you have installed?