My mac keeps fast forwarding

My iMac keeps fast forwarding at random times, both with audio files in iTunes and video (iTunes, quicktime, vlc). Ive tried deleting files and re loading/ re importing them and it keeps happening.

I was watching a video in VLC yesterday and it worked perfectly, left it over night and now it fast forwards when i press play and then i can't even pause it - it just keeps fast forwarding despite the fact the play/pause button indicates it has paused.

Please help, i need my audio and video files to work for my Uni thesis and its seriously stressing me!