NEED HELP!!! Event ID 9175, Event ID 9518, Event ID 8197 keep coming out - Microsoft Exchange

I need solution for my exchange server 2000 IS, the stores
can't be mounted because of these ERRORS. Help Me pls!!!!

Event Type: Error
Event Source: MSExchangeSA
Event Category: MAPI Session
Event ID: 9175
Date: 07/05/2004
Time: 17:50:34
User: N/A
Computer: SERVER03
Description:
The MAPI call 'OpenMsgStore' failed with the following
error:
The Microsoft Exchange Server computer is not available.
Either there are network problems or the Microsoft
Exchange Server computer is down for maintenance.
The MAPI provider failed.
Microsoft Exchange Server Information Store
ID no: 8004011d-0526-00000000

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Event Type: Error
Event Source: MSExchangeIS
Event Category: General
Event ID: 9518
Date: 07/05/2004
Time: 17:39:43
User: N/A
Computer: SERVER03
Description:
Error 0xfffffc01 starting Storage
Group /DC=ID/DC=CO/DC=NPP/DC=PUSAT/CN=CONFIGURATION/CN=SERV
ICES/CN=MICROSOFT EXCHANGE/CN=NPP/CN=ADMINISTRATIVE
GROUPS/CN=FIRST ADMINISTRATIVE
GROUP/CN=SERVERS/CN=SERVER03/CN=INFORMATIONSTORE/CN=FIRST
STORAGE GROUP on the Microsoft Exchange Information Store.
Storage Group - Initialization of Jet failed.

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Event Type: Error
Event Source: MSExchangeFBPublish
Event Category: General
Event ID: 8197
Date: 07/05/2004
Time: 17:28:53
User: N/A
Computer: SERVER03
Description:
Error initializing session for virtual machine SERVER03.
The error number is 0x8004011d. Make sure Microsoft
Exchange Store is running.

For more information, click
http://www.microsoft.com/contentredirect.asp.