Udimm slots now filled, 64 bit PC not showing new memory

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Udimm slots now filled, 64 bit PC not showing new memory

Help please!

I have a Packard Bell IMedia S3810 which can take 8GB.

Factory standard Ram sits in the two slots, 1GB and 2GB.

Next to these are two slots labeled UDIMM. 

So I checked the crucial site whic said there was a twin pack of UDIMM 2GB modules, bargain!

But now installed and seated properly and the PC can't see them, and its not acting like it has 4GB more ram when I'm trying to use Adobe Premiere Pro.

Any suggestions why?