Media Issues

After installing a plugin, I am suddenly unable to view my media library – the images still exist on the website, but all I can see are grey squares with a folded over top corner. The sizing of thumbnails etc seems to have been altered when I look at my site. When I upload a new image, it seems to work just fine.

I have tried disabling all plugins, reinstalling the latest version of WordPress, all to no avail.

I am not very tech savvy in this department, so any help would be much appreciated!