In order to bring up the ability to run the %appdata% command, press the windows button (next to the alt key, two along from the space bar [ish]) and the letter R.

Find your .minecraft folder. Before you delete it, feel free to copy some of the things you love dearly, eg maps, skins, resource packs, worlds, so that you can paste them back into your .minecraft file at a later date.

Searching some of the key words above should bring up a few results, some of which may help you.