new video card problems

[Bill Stanley]

I just upgraded my video card from a Nvidia 420 with 512 MB of video ram 
to a new Nvidia GTX550Ti with 2 GB of video ram.  I dual boot and 
Widnows uses this card OK (this rules out hardware problems) but I can't 
get the GUI running when I boot to Linux.  I am dumped into the command 
line and since I am not as proficient with the command line, I do not 
know what commands I have to use to get the new video card to run.  Of 
course, without the GUI, I also can't visit the usual help sites.

Since they are both Nvidia cards, I didn't expect much problems and 
hopefully it isn't much of an issue.  Could it be the 2GB of video RAM?
Please let me know what CLI commands will get the GUI up and running.