can anybody analyse this position?
why 4...e6 is not played?

What's the White Queen doing on g4?

This position looks perfectly fine for black.

That said, what is that queen doing over on g4? It just doesn't belong there. I'm assuming 1. e4 d5 2. exd5 Qxd5 3. Nc3 Qa5 4. d4 e6 5. Qg4 lead to this position, let me step back one full move:
1. e4 d5 2. exd5 Qxd5 3. Nc3 Qa5 4. d4

One of the main ideas in the Scandinavian, Alekhine Defense and Caro-Kann is to get the Bc8 out easily. As you may know, that's a problem piece in many defenses. Playing e6 immediately puts that idea out of business. If 4. ... e6 5. Nf3 black cannot pin the knight with Bg4 as he sometimes wants to, Bf5 lines are also out now.
In and of itself, 4. ... e6 isn't bad, it ends up in an odd line that sometimes comes out of the Exchange French (where the French defender doesn't want to play exd5) it's just inferior to 4. ... Nf6.

so if i want to play 4...e6 all the time what can i do for 5Qg4 and where should i castle,my plan was 0-0 until 5Qg4 now i must play lets say 5...Nf6 6Qg3 g6 with Bg7 and then 0-0;Nf6 6Qg3 Nh5 7Qg4(or else)Bb4 and 0-0;Nf6 6Qg3 Ne4 7Qg4 f5 etc or 6...Nc6 7Bb5 etc.
what is the best line against 5Qg4?

thanks!

Um, we can't look into your mind and know what you were really asking. If I understand correctly, your question was twofold.
-1. After 1. e4 d5 2. exd5 Qxd5 3. Nc3 Qa5 4. d4 why isn't 4. ... e6 played at master level? Is it any good?
-2. How should I meet 5. Qg4 in the aforementioned line?

If this is what you're asking then here goes:
1. Play 4. ... Nf6 and follow the big boys. For the following reasons:
-a. The e6-move comes in later anyway.
-b. There are lines (when white wonders off the main paths) in which black can get in e5 in one shot, e6 wastes a tempo in that respect.
-c. As I mentioned, the Scandinavian has in common with the Caro-Kann and Alekhine that the bishop on c8 can slide out easier than in other defenses. The immediate e6 takes away the 'threat' of Bg4 when Nf3 is played and the opportunity to play Bf5 soon.
-d. You prematurely set up the layout of your pawn chain. Not a particular good idea either, keeping white in the dark for even one more move has advantages.

2. 5. Qg4 isn't best. I can think of 10 moves that are better than Qg4. White is better off playing 5. Nf3 (as I said before, no pins), 5. Bc4, 5. Bd3, 5. Bd2, 5. Be2 or some such.
After the dubious 5. Qg4, black has what he wants, more or less an equal game. Let me analyse.

[Root: 1. e4 d5 2. exd5 Qxd5 3. Nc3 Qa5 4. d4 e6 5. Qg4 Nf6]

6. Qg3
Your line first. I would suggest 6. ... Nc6 and white will have some trouble proving an initiative, in fact black has pull on the d4-pawn.
7. Be3 would be a catastrophic blunder because of 7. ... Ne4. Or 7. Bd2 Nxd4 8. O-O-O Bd7 and black is running off with the pawn with insufficient compensation for white.
Another variation is 7. Qg5 Qb6 8. Nf3 Bd7 9. Bd3 O-O-O and there are no problems for black.

6. Qg5
A little better for white is 6. Qg5.
6. ... Qxg5 7. Bxg5 and white gets a nice edge because of the lost tempi.. That's no good.
6. ... Bb4 7. Qxa5 Bxa5 8. Bd2 O-O and you're okay.
6. ... Qb6 7. Nf3 Bd7 8. Be2 Nc6 is a little muddier. I think white will at times drop the d-pawn for development, key for black is to keep the royal family safe.

No problems for black really. If everyone played this in the Scandinavian, I'd (still) play it.