Hi, Sadie G, & welcome. First, you don’t give us an url to your site, which is often helpful.
2nd, generally when this sort of problem occurs, renaming your theme folder (i.e., instead of yourtheme, rename it to yourtheme1) may help. That will break your site for a bit, but it might allow you to log in & change the theme, which will restore your blog. Also renaming the plugins folder, e.g., to plugins1, can prove beneficial as well if renaming the theme folder didn’t work.
If renaming the plugins folder resolved the problem, then rename the plugins folder to plugins again, but rename each plugin folder to something different, leaving only 1 plugin w/the proper name, then try logging into your site & see if it’s still ok. Keep doing that till you find the plugin that caused the problem & rename it back to plugin1, or simply delete it. It won’t be operational, but it won’t break your site.
You’ll need to use either FTP (& hopefully secure FTP) or your hosting control panel to do this.
Please let us know if that helped or not. If not, please do provide a site url.
