Photo quality falls when importing from CS5 raw to photoshop

I recently updated my computer and reinstalled PS CS5. Under my new install, pictures processed in raw become grainy (it is very difficult to explain but that is a good enough approximation) when opened in Photo shop. I didn't have this problem until the reinstall. I seem to have set the colour spaces correctly, using both Pro photo in Raw and PS. Ironically, I have just started to take on some paid assignments so it couldn't have come at a worse time. All help wonderfully appreciated.

Many thanks in advance.