timeline lag premiere elements

hello i am going to keep this simple.

so when i go in to edit something on the time line (add effects ect.) it lags not hard core but you can see it.

If i stop the video for 1 second and start t again it fixes the problem.

I am not sure if this is something that has to do with my hardwear or softwear.

I currently have a mac.

2.5 GHz Intel Core i5

16 GB 1600 MHz DDR3

Intel HD Graphics 4000 1536 MB

2.5GHz 500GB 5400-rpm hard drive

i got about 9 days to figure this out before i can't take my computer back