I think the answer is yes
Can you still access localhost and phpmyadmin? (I'm guessing the ISE 500 problem rears its head when you access your WordPress site(s)???)
Start phpmyadmin, locate the database for your site. The table you want is xxxx_wpoptions
the option_id is 32 - permalink_structure - delete the longtext value that might look like "/archives/%post_id%"
leave the longtext field empty (that's what it is when WordPress permalinks are set to Default) save the value with 'Save' and 'go' option on the phpMyAdmin page.
Now your site (if that IS the problem) should work
Here is a note to self for you - "this is why you should never do development without daily backups"
ADD THIS plugin "WordPress Database Backup" and USE IT!