Blank Screen !!!

Blank Screen !!! (Windows Vista Ultimate 32-bit)
After i changed the memory of my system to 512 MB there is a Blank White screen after the Welcome screen in can move the mouse but nothing else can be seen....in safe mode the screen is Black with safe mode on all the 4 Corner but nothing else...i tried to remove the 256 GeForce 7100GS Graphic card and tried to run the system in the intgrated Video and still the same issue....is it only because of the low RAM.........

How much memory you had on your computer earlier?
And why are you trying to run Vista on just 512 MB?
You should have atleast 1 GB. And you can try a startup repair to boot to desktop.
Click here: http://www.vistax64.com/tutorials/91467-startup-repair.html