I have a problem with instrumental tracking into vocal track

OK, I'll try and explain this, When I try to record my vocals the instrumental comes through. I already had my instrumental loaded in the first track, when I added the 2nd for my vocals the instrumental came through, I have already checked my sound card settings and its not on play all or stereo mode. there is something else too, My mic wil not work in the microphone jack on the front of the computer, it only plays in the input jack. when I loaded audacity it did the same thing on it, the instrumental played through both tracks, but when I used the mic slot it worked on audacity but you know that when you record using audacity you can't hear yourself while you record your vocals which is why I went to try reaper. I hope this makes since. I just trying to record the vocals without the instrumental coming through the 2nd track. Any help would be greatly appreciated.

Could you post a pic of the reaper project, so that tracks are visible, maybe take a pic of track I/O routing too.

my camera is not working wish I could post a pic, It just should not be this difficult to record vocals, I have the instrumentals I just want to record my vocals, does anyone have a link to a video that shows the steps for a set up like this. Just laying a instrumental then vocals that shows the set up, like the I/O settings and nothing fancy, like I said I'm just trying to record my vocals over a beat.