Losing and adding seconds and smaller

[TenshiOfMercy]

This is very weird but recently my Adobe Premiere Pro CS3 have been fuckt up.When I have taken the piece that I want it drops or adds seconds and smaller parts ((Don't know the English word ))
The original clip it does the same thing too so sometimes I can't even
get the clips I want

Anybody else who have had this problem and know of a solution to it??