I have been using Expression engine for a few months now and I’ve never encountered this before. I’ve made a change to one of the templates, which was really basic html and now I can’t access any of the pages except the login page. I am recieving all these MySQL errors. I don’t know much about PHP, but is there a way I can get into the back system to change the file back to the way it was, since I can’t log in and change it?

The type of error I see is:

MySQL ERROR:

Error Number: 1146

Description: Table ‘dbfvtn.exp_templates’ doesn’t exist

Query: SELECT SUM(exp_templates.hits) AS total FROM exp_templates, exp_template_groups WHERE exp_templates.group_id = exp_template_groups.group_id AND exp_template_groups.is_user_blog = ‘n’

Have I lost everything from my site?

Check in phpMyAdmin or other database management tool that your host provides with your account, and first verify that the table does still exist in your database.  Most likely you just need to run a repair, which is an available function of phpMyAdmin and other db management utils (including ExpressionEngine’s own SQL Manager, but if it’s not letting you log in, you’ll need to use one of these other tools).