Control Panel and Sites

So, about a week ago I started to get sites are down then up, I rebooted the VPS from the vendor and everything started working again and then it wouldn't. I asked the vendor if there was a problem with the node, he responded I can ping the VPS so not my problem. I think there is a problem with the VPS but can get them to respond anymore now. As I write this I can SSH into my VPS and the webpanel is working

Any ideas what to do, TY

What do the server logs show?

You may want to run external monitoring software; either simple ping or more involved site monitoring with SMS or e-mail alerts.

HetrixTools & UptimeRobot both offer free monitoring levels.

What do the server logs show?

Where would I find that?

http://wiki.centos-webpanel.com/service-log-paths

But as overseer mentioned, monitoring the server with a 3rd party, and see if there is a pattern.
Or get notified when it stops responding, and see if you can access it at that time via SSH, web, etc.