Get an SSD. Photoshop will open much faster.
Also, the larger the drive C: is, the more sparse (fragmented) the files will be, which will obviously take more time to access. This is especially true for HDDs, SSDs not so much. Try to regularly defragment C:, or you could use Diskeeper (or similar) to run in the background. It may take some time when you save a file, but at least it's saved in the optimal place... I remember I had to temporarily stop the process (from the Services lists), because quick saving in games would annoy the crap out of me. And believe me, I save often.
Last but not least, check for viruses.