I addressed the aspect of your grounstrokes above first because it is very important that you understand what is responsible for what causes topspin in tennis.
Hard, penetrating topspin occurs from hitting the ball from "low to high".
Hard, penetrating topspin does not occur from trying to "brush up on the ball" - adding it on with a wrist movement.
Trying to brush up on the ball will only result in wristy, spinny shots that don't seem like you've hit them very hard.
So go back and understand what is going on in the correct way to hit topspin in forehands and backhands.
Then you can go about solving the problem you have in not hitting a forceful topspin serve.
In the posted video you are not hiting "low to high" in your serve.
You have too little rear shoulder drop going into your trophy pose, and subsequently too little ability to drop the front shoulder as the hitting shoulder comes up - too little vertical shoulder over shoulder action.
Instead your shoulders are being swung from right to left in a horizontal plane [and as a symptom of this you swing your rear leg around from right to left, rather than kicking your rear leg back like the pros].
Jim McLennan of TennisOne explains exactly what you are doing wrong in this video:
http://www.youtube.com/watch?v=lTRvxaBMh8s
[He stresses this also can cause a rotator cuff shoulder injury, but you are swinging your shoulders like the "amateurs he mentions, not like the "pros".]
The result of this type of swing is that you are hitting the ball straight forward without any "low to high" action.
Instead you want to be hitting the ball while your racquet is still going up:
Here's how to do it:
You want to get into a steeper shoulder angle in your trophy pose, and use a vertical shoulder over shoulder action to bring your racquet up the back of the ball to impart topspin.
As you release the ball, keep bringing your tossing arm up and up and up until it is held straight up (pics 1-9) as you go into your trophy pose. This gets the rear shoulder down and gets the tossing shoulder up.
Also notice that by the trophy pose (pic 9) as seen from the side the body is in the "shape of a bow" with the front hip over the baseline.
In pics 10 - 13 the rear shoulder is rapidly raised (and the front shoulder rapidly dropped straight down.
(At the same time the "bow shape of the body is reversed.)
What this causes is that right after pic 13, the racquet is still moving up low to high, even as the ball is struck.
This "low to high" motion of the racquet imparts the topspin you are looking for, even as you give the ball a powerful smack with a pronation movement with your arm.
I hope you follow this and are able to incorporate it into your serve.
