Sony Vegas Editing problem

I recently installed Sony Vegas Pro 8.0, which at first worked fine.
But now its developed a problem I cant solved despite checking all settings! When editing in timeline, having split the clip into the segments I want, the edited clips which are supposed to be able to be moved around in timeline, just refuse to move. When I move them to required position they just jump back to the original position where they were before when I split them so nothing can be joined moved or whatever. I even tried re installing Vegas but the problem persists. So at my wits end basically- any help be most welcome!