Sorry for the delayed response.
http://www.leadtek.com/3d_graphic/wi..._myvivo_1.html
Why were you trying new drivers?
"then installed latest NVIDIA drivers and also tried the old leadtek drivers"
Thru all these processes are you deleting the previous drivers?
Via the Device Manager as well as Add/Remove Programs?
Are you doing this in Safe Mode?
You say that Windows loads but that there is no display.
Can you clarify: What do you/ don't you see?