Peavey Rage 158 (Transtube Trouble)

Hello, all, I'm new here. I was hoping you could help me with a little problem with my amp...
When it's all plugged in, there's no sound coming from anywhere. The headphone jack's contacts are pried up a little bit, but when I push them down (when there is nothing plugged into it), there's a nasty crackling, popping sound coming from the speaker. One time, i plugged it in and it was working fine, but it quickly degraded back into this state. i have not been able to replicate that situation. i haven't found any loose connections, nor is it the guitar/cord i'm using.