effects loop isn't working right on my peavey tour tnt amp

[cloudyorchestra]

I have a pedal board all set up and when I hook up my to my send and return inputs it wont play my effects and it doesn't make any sound and if I turn my pregain all the way up it'll make sound but just a heavily distorted sound.

I've checked all my cables and they're all good but can anyone tell me what is going on?

 

[Downunderwonder]

Two possibilities come to mind.

Fx out going to pedal loop out?
Loop contacts corroded? Normally the amp would have cut out if it is a series loop.

If it is a series loop any dud cable or pedal will kill output.

 

[BassmanPaul]

IMO a pedal board with instrument level pedals should be placed before the input of the amp. The FX loop tends to be more for line level units.