Migrated Servers now 500 Error _db_error_page('Access denied f...') Moved servers, copied all files and database and set server settings to match old server. Updated settings.php with new database credentials and tripled checked them for the correct information. Console gives me a truncated error message so I don't know the exact problem.

[21-Feb-2019 15:02:21 UTC] PHP Fatal error:  Uncaught Error: Call to undefined function ereg() in /public_html/includes/file.inc:1034
Stack trace:
#0 /public_html/includes/file.inc(1032): file_scan_directory('themes/pushbutt...', '\\.info$', Array, 0, true, 'name', 1, 1)
#1 /public_html/includes/common.inc(2888): file_scan_directory('themes', '\\.info$', Array, 0, true, 'name', 1)
#2 /public_html/modules/system/system.module(868): drupal_system_listing('\\.info$', 'themes')
#3 /public_html/includes/theme.inc(493): _system_theme_data()
#4 /public_html/includes/theme.maintenance.inc(51): list_themes()
#5 /public_html/includes/bootstrap.inc(1221): _drupal_maintenance_theme()
#6 /public_html/includes/database.inc(176): drupal_maintenance_theme()
#7 /public_html/includes/database.mysqli.inc(78): _db_error_page('Access denied f...')
#8 /public_html/includes/database.inc(15 in /public_html/includes/file.inc on line 1034
and set server settings to match old server


That process went wrong - ereg() was removed in PHP 7.0, and Drupal 6 couldn't have been running on a version of PHP that high on your old server.

I think PHP 5.3 is about as high as you're likely to be able to get with Drupal 6, you should get your server admin to downgrade to that version ASAP.