GUI Miner 0 shares accepted after upgrading the GPU

[nskjgfhgh]

Sorry to be posting in this category but im not allowed to post anywhere else. GUI miner was working fine untill yesterday when i upgraded my graphics card to a  XFX radeon HD 6750. I have installed all the drivers but since then GUI miner reports a 140Mhash/s 'speed' but in about 8 hours i have had no accepted or stale shares. Any ideas?

[lbsmining]

Are you using the OpenCL miner?

It's possible that you were using a CUDA miner before, and it won't work after switching to an ATI card.

[nskjgfhgh]

Yes i am using the OpenCL miner. Before i was using some old ATI radeon card and was only getting 7Mhash/s. Any ideas?
  I am going to remove all the related drivers and try again but please let me know if you have any other potentially useful info.