This image looks like you have a pretty high resolution monitor.
There are only two things I can think of that would make the icons appear to have become smaller:
1) You changed the resolution settings for your monitor in the operating system. In which case, they will look smaller if you don't make any other changes.
2) You changed the setting in SOLIDWORKS from using large icons to using small icons. This setting is in Tools, Customize, Toolbars. Even if you did change your resolution of the monitor as per #1, you can make the icons larger by choosing the large icon size in customize.
I hope this helps,
Thanks, I really changed to small icons on sw.