Is it dead dead, like not working at all? Make sure you read the manual about how to set the loop to work. I know I bought a DL4 off Craigslist and it works...but the looper is something you have to read about to get the idea about it.

If it still gives you problems, contact Jim at http://r3fx.com he modded my DL4 and is extremely knowledgeable about the DL4.