Precision 7540 GPU Upgrade

Hi all

I bought a 7540 laptop about 18 months ago with the standard Intel GPU installed. I decided to take a punt at upgrading the GPU to an Nvidia T1000 to get better graphics performace. I managed to find the GPU on eBay that also came with the DGFF cable. Good news so far until I went to fit it only to find I did needed to upgrade the Heatsink as well. Again, I managed to find one on eBay. I completed the GPU upgrade along with replacing the Heatsink only to find that both the BIOS and Windows do not see the new GPU. Any ideas (short of a faulty GPU or cable) on what I could have missed? Thanks. Any responses appreciated :-)