Sliced and trimmed video clips are pixelated and distorted - help

Hi, 

I have been making a video for weeks that is made up of many different footage clips which I sliced up and put together, however now when I play it, in the editing software (I have not exported it yet) parts of the different clips look pixelated or discolored for a few seconds.  I have tried slicing off the bad part and extending the footage again and same thing happens. 

Does anyone know how to fix this? It will make the video look bad if this happens throughout it and the time it will take to replace the footage again would make me cry.  I've searched and there is nothing online that talks about this.

Thank you for your help!