Hi Kylie75
Have a look at my other posting where I have suggested a quite good FREE converter program.
As you are finding MPEG4 files a bit temperamental on your PC using VP (and I think any other editing program will be similar...I have tried several) Have a go at converting to MPEG2 format. Unless you are going to output to big HD TV screens you won't notice much difference..it's still HD. With this software you can simply try a different setting and find what looks best. It's pretty foolproof.
Get it first and come back here if you are puzzled.
The free software I have suggested works fine for me and is not difficult to run and the results seem OK.
Nat