Hi Carla,
if you get a band with your PCR, you can see the marker on the gel but
there is no signal after the digest, you most likely have a DNAse
somewhere in your system. Be sure to include sufficient and suitable
controls for the digest (in your case, PCR product on the gel should
be enough). To locate the possible source of DNA contamination, you
might want to leave out *one* component of the digest at a time. Maybe
it's more straightforward to get everything new (water, buffer) than
to try around for a long time.
HTH
Wo
