Because a very, very similar issue happened to me when I updated, and then was fixed when another update came out and I grabbed it.
Well I'm running Dolphin on Windows 8.1 and am not encoutering any problems.
Have you tried running other Dolphin versions? I am using 4.0.2 (stable). Newer versions than 4.0.2 will of course be better, but if they don't work give the stable version a try.