If other instruments are detected, then the GPIB card is okay. Try switching cables. Sometimes you'll find a bad one. It's more likely a setting on the scope. First, make sure the scope has a unique address (non-zero). Then, check the manual to see if there's a setting on the scope to actually enable GPIB communication. I'm not familiar with this model, but some instruments require you to turn it on or if it supports multiple protocols (i.e. serial, GPIB, ENET), you have to rurn on the one you want to use.
