Hello,
make sure, that you removed the driver of your old card completely.
Then check out for the newest chipset drivers, inlcuding AGP or PCI-Express device driver.
Install them and update the needed devices.
Then make sure that DirectX is Version 9.0c, if not, download it from Microsoft.
The last step is to install the proper and newest driver for your new graphci card.

Note: It may be neccesary to restart your system during thei sprocess several times.

If this does not solve the problem, make a RAM test.

old_bill