Should I use LAMP or Windows?

Hi, I stumbled on your site and I am thinking about starting a website. I haven't received a good answer about what I should use to build it, so I thought I would give it a shot.

I am a windows guy. I know .Net and ASP and how to build web sites using that stack. But I notice most sites use LAMP and that's what most people talk about using. What's wrong with using Windows?

.Net Programmer