I am getting 404 error on clicking any link

Hi,
Recently I tried optimizing my site by using various plugins (js and css compressors) and a few of these didn’t support my version of wordpress. Now when ever I click on any link including login and register I get a 404 not found message.

I tried uploading anew .htaccess file and deleted the plugins using ftp but I am still getting those errors. Kindly help!!