PCR don't work

[cilia jonas t2814]

hello netters
I try to make a PCR with a lambda-ZAP-Phagenpool
One primer is T7, hybridizing to a sequence common to all phage DNA
the other ones are genspecific (20-25 bp long). I can amplify with two 
genspecific 
primers a short stretch, so I know it is there in my phagepool.
A PCR with another (strange) genspecific primer and the T7 worked 
well, 
too. But I fail  to amplify something between my genspecific primer
and the T7
I'm very grateful for any suggestings and ideas
Sincerly  Cilia