My DM800se just reboots itself

Hi guys!
I have had my dm800se for a few years now and suddently it started to reboot from time to time. Let s say I am watching a movie and it just reboots itself changing even the language settings of the channel. Some times it does it often others it might do it once a day. When it reboots it always goes to the start up preset channel. Even if I turn it off from the remote it does the same thing, so in other words it is always turned on.
Do you know what it could be to make it act so weird?
PS: I tried disconnecting the internet and it isn t that the problem
Thanks

Thanks Inspiral! Do you know where I can get instructions on how to do that?

Just Wanted to post an update for people that have the same problem I had.
In the end it was the AC adapter that was the problem. After changing it the issue stopped. The ventilation system stopped making a lot of noise and the diseque switch started to work properly. Hope this info will help others in the future