Right Speaker input not working!

I recently bought a Soundscraftsmen 3000A Solid State Stereo Receiver along with a Kenwood KD-3100 turntable.  The issue I am having is with the speaker inputs. It has inputs for 4 speakers.  The two on top are for left speakers and the two on the bottom are for the right speakers.  The left speakers work perfectly fine.  The bottom inputs for the right speakers are the issue.  They will work for about 5 minutes and then it will sound like the speakers are blown out.  Everything is wired correctly.  When I wire both speakers to the left they work perfectly fine all day.  It's the right speakers that are the issue. Check the fuses too and they're brand new. Would anybody know what might be wrong?
Those are speaker outputs not inputs. Get some electronic contact cleaner, with the amp unplugged, pop the bottom plate off and spray some in the speaker selector switch. If you don't want to do that, you might try rotating the switch all the way to the right and back to the left a couple dozen times with the amp off. You might try that with the volume & balance also. These controls get dirty over time and can create these problems.
Cleaning contacts can be good, however, playing for a few minutes, then cutting out is not a dirty contact issue IMO.

Speakers, two pairs? Do you have the receiver's manual?

Unless you have a selector up front for speakers A, or B, or A+B, it may be that you are only supposed to use one, or the other speaker outputs, not both.

Often they are for different OHMs, i.e. a pair of outputs for 8 ohm speakers, or, use the other pair of speaker outputs for 4 ohm speakers.

Efficient speakers, high sensitivity? 

I would hook up only one pair of my most efficient speakers, see how it is. Even small speakers from your office temporarily, just to see if it makes a difference.
dill nailed it. Only thing to add is if you carefully slowly and slightly tap or turn the selector switch while the speakers are playing and it causes the sound to cut in or out that is confirming its the switch and not something else.