SQL server connection problem

[webapp]

Hi……..

I have installed SQL Server on my PC….it used to work fine………
Now I was using it after long time.It gives the following error once I click query analyzer.

Unable to connect to server NEO

Server:Msg 17,level 16,State 1
[Microsoft][ODBC SQL Server Driver][Shared Memory]
SQL Server does not exit or access denied.

When I click local nde of sql server group the following error occurs……

A connection could not be established to (local)

Reason : SQL Server does not exit or access denied.
ConnectionOpen(Connect())..

Please verify SQL Server is running and check your SQL Server registration properties

[dglienna]

Make sure that it's started, like the msg says

[webapp]

i am not able to start SQL Server Service Manager.
after clicking that green button of start/connect, it still shows the stop red sign only.

and then later the above mention error

plz help.........