What might have cause for vCenter Server 4.1 Update 1 to suddenly stop?

[Cloud2011]

When we try to ping it we still received response from it and then it suddenly sends Timed Out reply.

The only activity that was informed to us was a power-off of one VM and an upgrade of View agent.

We decided to restart vCenter Server vm but it got stucked at 95% for a long time, so we decided to restart the vm directly through the host.

We also restarted the management agent through the host but vCenter is still unreachable.

So we ended up restarting the host that reslved the issue.

Any insight on what must have caused the vCenter to stop responding?

[weinstein5]

Is the database store locally or on a seperate database server? - Make sure the vCenter server is communicating to the database server

[Cloud2011]

The database is stored locally as we only have small environment.

[Cloud2011]

Error found is "Lost accessto volume ... due to connectivity issues. Recovery attempt is in progress and outcome will be reported shortly.