2x2GB RAM P5KPL-VM SE

I have got the mobo above in a small form factor case running my media servers apps etc.

I have been running fine with only 1x2GB of 800mhz RAM but as I was needing to think of something for the kids to buy me for my birthday I decided to get a further 2GB. I now have 2x2GB of RAM. I'm running Vista 32 bit and the RAM is the following:-
http://www.eclipsecomputers.com/product.as...e=ME-D2-2048-80

The second stick is not being recognised by Vista and when I run cpu-z the slot shows as empty. Does the RAM have to be Dual Channel for 4GB to register?

I havent got into swopping the sticks yet as its a bit of a pain as the PC is on 24/7 and its small form factor so fiddly. Before I do therefore I just want to make sure that it should work.

Either way it may have to be turned off mate.... Have you tried clearing the CMOS? You might have to do a swap around on the sticks to see if it makes a difference too. Its hard to say if it will definitely work or not. You could have a bad stick, you may need a BIOS update.. your voltage for the RAM may be too low etc etc...