I have a Linux server. In the beginning it ran well, after several days, I cannot see anything through KVM screen, it was blackscreen. Then I reboot the server. I find the heartbeat run out some error and warning. I found no kernel crash report. I need suggestion. What can result in blackscreen? Which point do i need to check in system log?

Jun 3 05:03:56 AAA heartbeat: [3743]: WARN: Gmain_timeout_dispatch: Dispatch function for retransmit request took too long to execute: 20 ms (> 10 ms) (GSource: 0xa720e80)
Oct 25 04:02:21 AAA heartbeat: [3761]: ERROR: Message hist queue is filling up (500 messages in queue)