Noob screwup on upload. Please help

OK folks, feel free to laugh at me as long as you help.

I spent weeks creating a blog on my PC using XAMPP. I have a domain, and created a subdomain to put the blog in. I changed the location in settings to the new subdomain, and copied everything under the wordpress directory to the root of the subdomain. I got an error connecting to database. I realized then that I didn’t have any clue about how to upload the database, or whatever needed to be done. So I tried to find the answer, but nothing I have tried seems to work.

Now here’s the kicker. I can’t get to my local copy anymore. When I go to localhost/wordpress, I get a oddly styled version of my page (which is really the 404 page). And when I try to login to the admin, it redirects me to my subdomain, and another error.

Can someone please at least point me in the right direction? Thanks.