Server 2012 issues on t20 server

hi all,

i have a server 2012 r2 which seems to be suffering from an intermittent hang. Sometimes it can go for a few days between hangs, others it is 2-3 hours. The logs show no events prior to the hang, just the usual start up ones when i reboot it.

Server is a dell t20, with 32gb ram, 3x 2tb drives in raid 5 on the onboard raid.

Server is only used to run hyper-v, initially i installed the standalone hyper-v server, but that had a similar issue.

Previously i ran esx-i on the server with no problems, so i don't think it is likely to be a hardware fault.

server is completely updated, including all drivers, and there seems to be no pattern to the hangs. Initially it seemed to be when the server was doing a lot of disk access, but a few of the recent hangs have been when it is doing nothing.

When it hangs, i cannot contact it by rdp, ping, or log in at the console.

Any ideas of where to look next would be appreciated. 

Thanks in advance.

Paul