Install OpenGL And/or upgrade your DirectX version, and make sure your graphics card drivers are up to date too.

I have no problems with OpenGL under Windows, I actually prefer it to DirectX in ePSXe There's also a possibility that you ran the game after the reinstallation in a higher resolution than you used to use, so that would also cause a slowdown in it. Maybe try 16bit graphics insteadof 32bit.