hooked up TT and preamp to receiver sound fades out after 4-5 seconds


I just bought a realistic lab 400 turntable and hooked it up to my receiver a pioneer vsx 56txi into the phono input. I will add that I am a total newbie to this. I got nothing no sound at all. I researched and bought a phono preamp behringer PP400. I hooked it into the phono in on the audio of the receiver and connected the ground wire and had sound for about 4-5 seconds and than no sound. I tried connecting to the cd audio in and same thing only sound for about 4-5 seconds. Everything else works fine regarding sound. Stumped. I would appreciate any suggestions you might have.
atrust
Well I set it up again like I did before and same thing. So I just started turning things on in different orders and it turned something on. I am getting sound now and it stays on. The only problem is it only comes from the rear 2 speakers and not the 2 front and center speakers. But at least I have sound and less hair. Thanks for all your suggestions which were all correct user error I guess or just luck. Thank goodness because this TT was almost going to have to grow wings to survive. Enjoy you day.
Seems like you have an issue with the set-up of the AVR.  I would do a hard re-set and work from scratch.