HELP! My wp-admin login page has disappeared!

Hi guys,

I don’t know what has just happened but I have just tried to login to my site https://www.PS3StockOnline.com/wp-admin and it tells me page not found.

I managed to get in through an old history page and my WP Stats and WP User Online isn’t working either – takes me to the same page. When I tried to delink a comment it took me to to the same page.

I deactivated and reactivated the above plugins and it still doesn’t work. What do you think has happened?

No one else has access, and all the settings are the same as on my other sites which are working fine.

Please help.