The file C:\ProgramData\VMware\VMware VirtualCenter\Logs\stats.log should contain error messages relevant to this.
We had the same issue with vCenter Server 4.1 and found the following frequently repeated error message in stats.log:
2010-09-30 18:25:58,420 pool-1-thread-1 ERROR com.vmware.vim.common.vdb.VdbODBCConfig Unable to get a connection to: jdbc:sqlserver://localhost\SQLVC;databaseName=VIM_VCDB;integratedSecurity=true as username= due to: The driver could not establish a secure connection to SQL Server by using Secure Sockets Layer (SSL) encryption. Error: The TDS protocol stream is not valid.
In our case this turned out to be a problem with the version of the Microsoft JDBC driver installed by the vCenter Server installer being incompatible with our database SQL 2008 R2 Standard. Caveat: VMware doesn't officially support this version of SQL Server yet. Our database is running locally on on our vCenter Server which is a VM running the Windows Server 2008 R2 operating system.
The vCenter Server installer uses JDBC 1.0 version 1.2.2828.100, which is designed for compatibility with SQL 2005. JDBC 2.0 adds compatibility for SQL 2008, and JDBC 3.0, which is the latest available from Microsoft, adds compatibility for SQL 2008 R2. Supposedly all of these are backward compatible. I downloaded JDBC 3.0 version 3.0.1301.101 from http://www.microsoft.com/downloads/en/details.aspx?FamilyID=a737000d-68d0-4531-b65d-da0f2a735707 for testing.
After stopping the vCenter services, I copied the downloaded version of sqljdbc_auth.dll for x64 to C:\Program Files\VMware\Infrastructure\tomcat\bin and the downloaded version of sqljdbc.jar to C:\Program Files\VMware\Infrastructure\tomcat\lib. After restarting the services, I got the error: "java.lang.UnsupportedOperationException: Java Runtime Environment (JRE) version 1.6 is not supported by this driver. Use the sqljdbc4.jar class library, which provides support for JDBC 4.0." It turns out that the JDBC 3.0 download also provides a file named sqljdbc4.jar. I copied that to C:\Program Files\VMware\Infrastructure\tomcat\lib alongside sqljdbc.jar. Still the same error, but then I deleted sqljdbc.jar and renamed sqljdbc4.jar to sqljdbc.jar, and finally the Performance Overview started working properly.
To complete my testing I decided to try JDBC 2.0 version 2.0.1803.100 also downloaded from Microsoft at http://www.microsoft.com/downloads/en/details.aspx?FamilyID=99b21b65-e98f-4a61-b811-19912601fdc9. Again I renamed the downloaded sqljdbc4.jar to sqljdbc.jar to avoid the error above. This earlier version, although not officially supporting SQL 2008 R2, does appear to work properly with the Performance Overview in vCenter 4.1.
