Unable to connect to server '(local)'; SQLServerAgent cannot start

Dear all,
as prework for the eVault 8 SP3 installation i changed the local admin pw and installed the SP3 Deployment Scanner, following a reboot.
Now the "SQL Server Agent" is unable to start, after start the service stops immediately.

OS: Windows 2008 Single Server, SQL 2005

In the Eventlog i got the following error:

++++++++++++++++++++++++++++++++++++
Log Name:      Application
Source:        SQLSERVERAGENT
Date:          05.11.2009 16:19:28
Event ID:      103
Task Category: Service Control
Level:         Error
Keywords:      Classic
User:          N/A
Computer:      vie-eu-arc-02.xxx.yyy
Description:
SQLServerAgent could not be started (reason: Unable to connect to server '(local)'; SQLServerAgent cannot start).
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="SQLSERVERAGENT" />
    <EventID Qualifiers="16384">103</EventID>
    <Level>2</Level>
    <Task>2</Task>
    <Keywords>0x80000000000000</Keywords>
    <TimeCreated SystemTime="2009-11-05T15:19:28.000Z" />
    <EventRecordID>8166</EventRecordID>
    <Channel>Application</Channel>
    <Computer>vie-eu-arc-02.xxx.yyy</Computer>
    <Security />
  </System>
  <EventData>
    <Data>Unable to connect to server '(local)'; SQLServerAgent cannot start</Data>
  </EventData>
</Event>
++++++++++++++++++++++++++++++++++++

in the SQL Agent Log:

++++++++++++++++++++++++++++++++++++
2009-11-05 16:55:03 - ! [298] SQLServer Error: 233, Shared Memory Provider: No process is on the other end of the pipe. [SQLSTATE 08001]
2009-11-05 16:55:03 - ! [298] SQLServer Error: 233, Client unable to establish connection [SQLSTATE 08001]
2009-11-05 16:55:03 - ! [000] Unable to connect to server '(local)'; SQLServerAgent cannot start
2009-11-05 16:55:03 - ! [298] SQLServer Error: 233, Shared Memory Provider: No process is on the other end of the pipe. [SQLSTATE 08001]
2009-11-05 16:55:03 - ! [298] SQLServer Error: 233, Client unable to establish connection [SQLSTATE 08001]
2009-11-05 16:55:03 - ! [382] Logon to server '(local)' failed (DisableAgentXPs)
2009-11-05 16:55:03 - ? [098] SQLServerAgent terminated (normally)
++++++++++++++++++++++++++++++++++++

i changed the User (local Admin, Domain Admin, other service Account)
on the SQL Server & SQL Agent same result.

I'am unable to start the SQL Server Management Studio, the Error:

TITLE: Connect to Server
------------------------------
Cannot connect to vie-eu-arc-02.
------------------------------
ADDITIONAL INFORMATION:
A connection was successfully established with the server, but then an error occurred during the pre-login handshake. (provider: Shared Memory Provider, error: 0 - No process is on the other end of the pipe.) (Microsoft SQL Server, Error: 233)
For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft+SQL+Server&EvtSrc=MSSQLServer&EvtID=233&LinkId=20476
------------------------------
BUTTONS:
OK
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Any Idea, where i could search the Problem?
br
Hermann