Fix WordPress Critical Error ASAP

My WordPress site is down, and I can't access the dashboard. I need an experienced WordPress developer to fix this critical error as soon as possible.

Requirements:
- Troubleshoot and resolve critical errors
- Restore access to WordPress dashboard
- No recent updates to plugins or themes, so likely not related

Ideal Skills and Experience:
- Strong knowledge of WordPress core
- Experience with debugging and error resolution
- Ability to work quickly under pressure

Please respond with your estimated time to fix and any relevant experience.