PCR from cell culture - to detect the presence of adenovirus (Aug/24/2007 )

I have to detect the presence of virus by PCR in adenoviral infections of a cultures cell that someone did.

She says she saw cytopatic effect (I didn’t see the culture), but I do PCR of two different genes direct from the cultures frizzed and warmed 3 times and I have a very little amplification in just one of the samples. Do you think it could be something in the medium that block PCR reaction? Do you think I should do DNA extraction first, or what could I do?
I use plasmid DNA as positive control and amplify very well

Thanks in advantage!!

If you have an inhbitor in the medium, maybe a dilution (1:5 or 1:10) will help.