Cable Box Resets Intermittently

At least once per day, the cable TV box gives the TV a green screen, shuts down, re-boots and then works for anywhere up to 24 hours or as few as 15 minutes.  I'm using a box we've had for at least a decade, with ROVI software.  The reset seems random, occurring at different times, different lengths of time between shutdowns, on different channels, and sometimes during recording as well.  The cable signal is working as other TVs using the cable signal (but not through the cable TV box) experience no problems.  We've ensured there is plenty of cooling air to the box and still no change in behavior.