You need to diagnose the problem and fix it.

Some things to look at:
1. Anti-virus / Anti-malware (on server and / or workstation)
2. Network connection (ensure wired if connecting via lan)

3. References to an old / deactivated server (check custom icons, Customization Directories)
4. Network connection (ensure wired if connecting via lan)

In my experience, the three most common scenarios for this are 1)your shared drive permissions or subnet have changed 2)resources on the database server 3)physical network issues.

Thank you. It turns out related to connectivity issue.