Login and admin 404 error

My site: http://www.thelostlondoner.com

Ok Im in desperate need of help here..

Problem: Yesterday I was toying around with some style.CSS and my internet at home was giving me problems so I kept restarting my mac and then all of a sudden BAM! my login and admin began re-directing me to a 404 error page.

I was not doing anything else other than doing some simple CSS which I doubt created this problem. The last time I had updated a plugin was yesterday day-time so I don’t think that created the issue either.

http://www.thelostlondoner.com/wp-admin
http://www.thelostlondoner.com/wp-login

Both direct me to a 404 error page at http://www.thelostlondoner.com/not_found. This happens instantly.

My website is still there and fine I just can’t get into the dashboard.

My failed attempts to resolve the issue:

– I’ve re-named both the theme and plugin folders to deactivate them to see if this was causing an issue. It’s not worked.
– I’ve cleared all my cookies and cache. Not worked.
– I’ve checked that all the files and folders are still there and they are where they are meant to be, they are.

To be honest I’ve only started this venture a month ago so Im still learning, and learning heavily from the 1001 things that have gone wrong so far. Therefore I’m a bit weary when it comes to editing much in my FTP. I haven’t tried re-installing wordpress as I’m not sure how to upload files to my FTP. Im worried I’ll just destroy it completely.

I’m using Safari which is all up to date.
I was using the latest update of WordPress.
DreamHost is my host. I am yet to contact them regarding this.

I have gone through every forum but some methods baffle me due to my inexperience. Therefore I need simple guide lines for a solution.
I am freaking out because I feel like I won’t get this resolved. Somebody please help!!