This is a known problem. The 722K - and I assume other receivers, especially with OTA add-ons - generate TOO MUCH HEAT, the lame fan's flow is misdirected towards the HDD instead of blowing the hot air out. To top it off, the cases only have vents on their two sides, with the top completely made out of one piece.
This causes excessive heat and the 105C capacitors cannot withstand the >140C temps inside the case. They puff out or outright blow.
From many posts here I have gathered, learned, and then put it practice, that reboots, freezes and the likes, are caused by bad capacitors. As time goes by, the frequency of the problem gets worse, until the unit is an anchor. Please SEARCH 'C194' and you'll find lots of posts about this problem.
I now use a small desk fan - though noisy - on top of my new 922 unit, which sits inside a wall unit but has a 4" opening in the back for the cables. I noticed the unit does not heat up as much with this aide, and I trust this unit will last me a few years. I had two 722K's that died, and could only revive one by replacing the bad caps. The other has two red blinking lights on the front panel and won't boot any more.