Delete Query: 14 minute to no response - sql-server

Question

I have a Sql Azure database, everything was good from last 6 months until today, when a simple
Delete from ListData where ListID=2323
fail to delete 7500 records out of 1.9 Million records after 14 minutes of running query. However Select query take less than 2-3 second to list them all.
Previously the delete works much like select and it usually take less than 20 second to finish delete operation. something is wrong today only.
Complete database size is 1.1GB where as we have Web edition set at 5GB so, we have plenty of space available.
Any idea what is going wrong? that delete has cause some serious problem in system which cause my client lose quite a money.
Thanks for any guide.
Edit: I do have couple of Index on table, but no trigger, FK or any other such thing in table. LISTID is foreign key [logically], and RecordID [another column in table] is auto increment id in Listdata table.
*Edit 2 *:
/****** Object: Table [dbo].[tblSalesListData] Script Date: 02-07-2013 11:45:14 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
SET ANSI_PADDING ON
GO
CREATE TABLE [dbo].[ListData](
[RecordID] [bigint] IDENTITY(1,1) NOT NULL,
[ListID] [bigint] NULL,
[SalesID] [bigint] NULL,
[UserID] [varchar](100) NULL,
[FirstName] [varchar](100) NULL,
[MiddleName] [varchar](50) NULL,
[LastName] [varchar](50) NULL,
[Address1] [varchar](100) NULL,
[Address2] [varchar](100) NULL,
[City] [varchar](100) NULL,
[State] [varchar](100) NULL,
[ZipCode] [varchar](10) NULL,
[WorkPhone] [varchar](15) NULL,
[HomePhone] [varchar](15) NULL,
[CellPhone] [varchar](15) NULL,
[Email] [varchar](100) NULL,
[DealerCode] [varchar](20) NULL,
[IsPrinted] [varchar](10) NULL,
[tag] [varchar](100) NULL,
[RecordDate] [datetime] NULL,
[CustomInfo] [text] NULL,
[SourceData] [text] NULL,
CONSTRAINT [PK_ListData] PRIMARY KEY CLUSTERED
(
[RecordID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON)
)
GO
SET ANSI_PADDING OFF
GO
ALTER TABLE [dbo].[ListData] ADD DEFAULT ('N') FOR [IsPrinted]
GO

Answer 1

Try to add index and change table structure -
CREATE TABLE dbo.tblSalesListData
(
RecordID BIGINT IDENTITY(1,1) NOT NULL PRIMARY KEY,
ListID BIGINT NOT NULL, -- NULL --> NOT NULL
SalesID BIGINT NULL,
UserID VARCHAR(100) NULL,
FirstName VARCHAR(100) NULL,
MiddleName VARCHAR(50) NULL,
LastName VARCHAR(50) NULL,
Address1 VARCHAR(100) NULL,
Address2 VARCHAR(100) NULL,
City VARCHAR(100) NULL,
[State] VARCHAR(100) NULL,
ZipCode VARCHAR(10) NULL,
WorkPhone VARCHAR(15) NULL,
HomePhone VARCHAR(15) NULL,
CellPhone VARCHAR(15) NULL,
Email VARCHAR(100) NULL,
DealerCode VARCHAR(20) NULL,
IsPrinted VARCHAR(10) NULL,
tag VARCHAR(100) NULL,
RecordDate DATETIME NULL,
CustomInfo VARCHAR(MAX) NULL, -- TEXT --> VARCHAR(MAX)
SourceData VARCHAR(MAX) NULL -- TEXT --> VARCHAR(MAX)
)
GO
CREATE /*UNIQUE*/ NONCLUSTERED INDEX IX_ListID ON dbo.tblSalesListData
(
ListID ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON)

Answer 2

I have a little bit of same problem. I did the following step. but be sure to back up the database before doing these steps.
Create another table with identical structure
Insert the data in new table of the old table
Drop the old table
and try again to see how much time will it take.

Answer 3

Thanks for #Dinup and #Devart that give me idea, though I didn't fully follow their word, but both of them guide me in direction where I found solution as :
Delete all Indexes based on my ListID.
Run my Query, it take less than 1 second now.
Recreate my indexes.
Happy Living.