I'm a bit of a noob at this, I flashed my dell bios and now am wondering how I activate windows & what version of windows should I install?
You can install any version you wish, but some may work better than others. What does it currently have or had as the case may be? What's the model? How about CPU specs, HDD size, amount of memory and etc? A hair more info would be helpful along with what you think you might want to do. Do you want a new OS or to restore the existing one or what?