The earliest demo of Microsoft Windows shows up in 1983, pissing off Apple, who then hurries up thier Apple GUI on the mac that came out in 1984, while Windows waited till 1985 and released Windows 1.01 to little fanfare. Windows was pretty much a failure of a MS-DOS graphical shell until about 1992, when Windows 3.1 took off and people started using it. That's REALLY where Windows started to gain marketshare. Windows 3.1 introduced a lot of people to the product, and with that version, it began to gain traction.

1995 is truly though, the year Windows became Mainstream. Windows 95 pretty much set the standard for everything going forward, and the world of computing would be forever changed to look like that from that point on. It also became a much less exciting and interesting place to be after awhile. Starting about Windows XP is when the beginning of Windows and Computers in general becoming boring, losing their niche, nerd/geek, hobbyist centric side-vibe while remaining professional so staunchly it made them interesting devices.