Graphics card not working after RAM upgrade

Hi there, i'm brand new to this forum, and relatively new to upgrading my computers etc.

Basically I have a Packard Bell iMedia X2415 which uses a Denver 10 motherboard. It comes with 3BG of RAM and a pretty lame graphics card. I decided to change the graphics card this week for a GeForce 9800 GT. Had some trouble getting windows to recognise it, not finding the drivers etc, but managed to get it going in the end. I even have dual screens atm because I had a spare screen and the graphics card supported it. There are only 2 slots for RAM, one with a 2GB card in and the other with a 1GB. I went to maplins (www.maplin.com) to get another 2GB card, took my current one with me to make sure I ended up with the right one.

Once I replaced the 1GB with the 2GB meaning I now had 4GB windows no longer recognized the graphics card, the resolution was all big, and only displaying on one screen. I can't find anything about nVidia graphics card anywhere in the control panel, I tried adding new hardware etc but no luck. I even put the CD in and tried to reinstall the drivers. I went to the website and reinstalled the drivers but still no luck.

If take the new 2GB card out, everything works fine (even dual screens), if I take BOTH the old ones out and just have the new one on its own, everything works fine. Basically anything upto 3GB with any combination of the cards I have, works fine.

I checked with packard bell and my motherboard supports upto 8GB so no problems there.

Has anyone ever encountered something like this before ? would appreciate any help

thanks

sam