Event ID 421 Source Windows Server Update

Event ID: 421
Source: Windows Server Update
Description: Connection to database failed. Reason=SQL Server does not exist or access denied.. Connection string: Data Source=servername\WSUS;Initial Catalog=SUSDB;Connection Timeout=60;Application Name=WSUS SQL Connection;Trusted_Connection=Yes;Pooling='true'; Max Pool Size = 100

Run the SVRNETCN.exe utilitiy
Select your servername\WSUS server and verify Named Pipes and TCP/IP are enabled. If they are not enabled, enable them.

net stop WSUSService
net start WSUSService
Monitor WSUS Service and see if it stops, monitor event log and see if this error logs again
If so, reinstall WSUS