New
#11
You made sure you removed all device software and then installed the most recent software for the new one clean?
What do you mean the card is "similar"? if it is a Radeon HD 6950, then the driver will be the same for all of the cards (despite the few differences between cards).
Here is the website: AMD Radeon click on the support tab and either automatically scan for the right driver or select the right one for your card. Make sure you remove every previous graphical software before you do this. Can remove via control panel, and you might even search for the folder that the previous software installed to, and delete it just in case there is any extra bits left over.
It could be a faulty card, you never know. If you still are having problems, try another card if you can (with removing previous software and updating the "new" card, once more).