I just recently bought a new computer and have a Geforce4 Titanium 4800se and I had the same problem, which I later found out wasn't a problem....
Which you may have done this, you took off the "Clone" setting.
I have taken some screenshots to show you how I fixed mine... if it doesn't help, check the manual that should have come with your vid card. Check in TroubleShooting and it has some directions there.
If you don't have the same Display Properties as me, because I checked the Manual and the directions were different from the screenshots you see above, then go Display Properties>TwinView
hope this helps,
-FireWolf