Assuming for a minute all the software is current and you have done resets which is what dish network will asked you first see if they will ship a replacement receiver rather then send a tech out all the hook ups will be the same. Also anything you've recorded if you can retrieve off the hard drive will go back with bad receiver. A tech in nc.
Is the receiver working well enough where you can access the diagnostics menu to see how hot it is running is and if so then go there via menu then 6 then 3 then go into counters and use the the remotes page button about 3 times and it will show you the the average temperature. I was wondering if you have any additional receivers and if so what but also I am assuming you have dp44switch.
OP, make sure your 722 has plenty of room to "breath".
I ran up on a 322 the other day that was constantly resetting and it was burning up because the guy had his VCR sitting on it. Once I moved the receiver so it could breath, it cooled down and worked okay.
If your 722 is cramped into a entertainment center, its air flow is likely restricted.
I think it's heat. I had the same problem with a 622. The DVR is always working, making lots of heat. Mine wouldn't reboot itself like you've described, it just would start acting goofy and not respond. It would lose audio (optical output) on the off-air locals. After a reboot it was fine every time. I put it on it's own shelf, put a few blocks under it to raise it up, and bored a few holes in the entertainment center.
These units (622/722 DVR) run hot. Put your hand on it after a few hours. I see fan attachments for them on ebay.