Fix Node.js Website Error

I need help to fix a Node.js website that I purchased for my business. It worked for a week, but now it crashes and shows an error when I try to launch it.

Requirements:
- Diagnose and fix the application crash/error.
- Restore website functionality.

Ideal Skills:
- Proficient in Node.js
- Experience with debugging and server configuration
- Knowledge of error handling and application deployment

Please provide a brief overview of your experience and estimated time to resolve the issue.