Peavey 5150 combo effects loop problem

Well in the past i have used it to record via the effects send and adding impulses and it worked great, but now when I try, almost no sound comes out of the loop. Does anyone know what could be wrong? Maybe time for new tubes? Please help!
 
dose the amp work fine aside from this?

the 1st thing i would do is check out the preamp tubes...if there's no problem there, find yourself a good tech