Query Too Slow

Excuse me in advance fo my little English.

I've got this stored procedure

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declare @Azienda as varchar(3), @Utente as varchar(20),
@DataDa as datetime, @DataA as datetime,
@AreaDa as varchar(3), @AreaA as varchar(3),
@LineaDa as varchar(3), @LineaA as varchar(3),
@TipoDa as varchar(3), @TipoA as varchar(3),
@FamigliaDa as varchar(3), @FamigliaA as varchar(3),
@ProdottoDa as varchar(20), @ProdottoA as varchar(20),
@AgenteDa as varchar(4), @AgenteA as varchar(4),
@NazioneDa as varchar(50), @NazioneA as varchar(50),
@ZonaDa as Varchar(3), @ZonaA as Varchar(3),
@ProvinciaDa as varchar(2), @ProvinciaA as varchar(2),
@ClienteDa as Varchar(12), @ClienteA as Varchar(12),
@DestinDa as varchar (5), @DestinA as varchar (5),
@TipoDestinDa as varchar(1), @TipoDestinA as varchar(1),
@FlagProdNoTarget as varchar(5),
@GrAcqDa as varchar(10), @GrAcqA as varchar(10),
@TipoCliDa as varchar(3), @TipoCliA as varchar(3),
@SettMercDa as varchar(3), @SettMercA as varchar(3)


Set @Azienda = '900'
Set @Utente = 'Eugenio'
Set @DataDa = '2004-01-01'
Set @DataA = '2004-01-10'
Set @AreaDa = 'UNI'
Set @AreaA = 'UNI'
Set @LineaDa = ''
Set @LineaA = 'ZZZ'
Set @TipoDa = ''
Set @TipoA = 'ZZZ'
Set @FamigliaDa = ''
Set @FamigliaA = 'ZZZ'
Set @ProdottoDa = ''
Set @ProdottoA = 'ZZZZZZZZZZZZZZZZZZZZ'
Set @AgenteDa = ''
Set @AgenteA = 'ZZZZ'
Set @NazioneDa = ''
Set @NazioneA = 'ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ ZZ'
Set @ZonaDa = ''
Set @ZonaA = 'ZZZ'
Set @ProvinciaDa = ''
Set @ProvinciaA = 'ZZ'
Set @ClienteDa = ''
Set @ClienteA = 'ZZZZZZZZZZZZ'
Set @DestinDa = ''
Set @DestinA = 'ZZZZZ'
Set @TipoDestinDa = ''
Set @TipoDestinA = 'Z'
Set @FlagProdNoTarget = 'Vero'
Set @GrAcqDa = ''
Set @GrAcqA = 'ZZZZZZZZZZ'
Set @TipoCliDa = ''
Set @TipoCliA = 'ZZZ'
Set @SettMercDa = ''
Set @SettMercA = 'ZZZ'

Select WSDFR.AreaCommerciale,
WSDFR.Agente,
WSDFR.NazDestin,
WSDFR.ZonaDestin,
WSDFR.ProvDestin,
WSDFR.Cliente,
WSDFR.DescrCliente,
WSDFR.GruppoAcq,
WSDFR.TipoCli,
WSDFR.SettMerc,
WSDFR.CDestin,
WSDFR.DescrDestin,
WSDFR.TipoDestin,
WSDFR.EsclStatis,
WSDFR.EsclTarget,
WSDFR.ValoreNetto,
WSDFR.TpDocum,
WSDFR.VCambioITL,
WSDFR.VCambioEUR,
WSDFR.MeseFatt,
WSDFR.Posizione

From W_St_DocFatt_Righe WSDFR
inner join UniP_Prodotti UPP on
WSDFR.prodotto=UPP.Cod
Where WSDFR.Dtdocum between @DataDa and @DataA and
WSDFR.AreaCommerciale between @AreaDa and @AreaA and
WSDFR.LineaProdotto between @LineaDa and @LineaA and
WSDFR.TipoProdotto between @TipoDa and @TipoA and
WSDFR.FamigliaProdotto between @FamigliaDa and @FamigliaA and
WSDFR.Prodotto between @ProdottoDa and @ProdottoA and
WSDFR.Agente between @AgenteDa and @AgenteA


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"W_St_DocFatt_Righe" is a view.

This query run on my SQL7 server and it takes about 10 seconds.
This query exists on another SQL7 server and until last week it took about
10 seconds.
The configuration of both servers are same. Only the hardware is different.

Now, on the second server this query takes about 30 minutes to extract the s
ame details, but anybody has changed any details.

If I execute this query without Where, it'll show me the details in 7
seconds.
This query still takes about same time if Where is


Where WSDFR.Dtdocum between @DataDa and @DataA and
WSDFR.AreaCommerciale between @AreaDa and @AreaA and
WSDFR.LineaProdotto between @LineaDa and @LineaA and
--WSDFR.TipoProdotto between @TipoDa and @TipoA and
--WSDFR.FamigliaProdotto between @FamigliaDa and @FamigliaA and
WSDFR.Prodotto between @ProdottoDa and @ProdottoA and
WSDFR.Agente between @AgenteDa and @AgenteA

or

Where WSDFR.Dtdocum between @DataDa and @DataA and
WSDFR.AreaCommerciale between @AreaDa and @AreaA and
--WSDFR.LineaProdotto between @LineaDa and @LineaA and
--WSDFR.TipoProdotto between @TipoDa and @TipoA and
WSDFR.FamigliaProdotto between @FamigliaDa and @FamigliaA and
WSDFR.Prodotto between @ProdottoDa and @ProdottoA and
WSDFR.Agente between @AgenteDa and @AgenteA

or

Where WSDFR.Dtdocum between @DataDa and @DataA and
WSDFR.AreaCommerciale between @AreaDa and @AreaA and
--WSDFR.LineaProdotto between @LineaDa and @LineaA and
--WSDFR.TipoProdotto between @TipoDa and @TipoA and
--WSDFR.FamigliaProdotto between @FamigliaDa and @FamigliaA and
--WSDFR.Prodotto between @ProdottoDa and @ProdottoA and
WSDFR.Agente between @AgenteDa and @AgenteA


It is a real puzzle!

What happen?

Is there someone that had such as problems and have the right solution?

Thanks in advance.
Bye
Eugenio