Sudden Error on IIS

Hi EE,

Lodged one our IIS webservers today to check on an issue and I got the following error message:

PROBLEM
Unable to connect to the database.
The error message returned was:
Timeout expired. The timeout period elapsed prior to obtaining a connection from the pool. This may have occurred because all pooled connections were in use and max pool size was reached.

Then I restarted the IIS Server

Now, this error message appears.

Runtime Error
Description: An exception occurred while processing your request. Additionally, another exception occurred while executing the custom error page for the first exception. The request has been terminated.

I rebooted the server entirely at this point but the issue still persists.

No updates have applied to the server recently. How would I go about troubleshooting this any assistance is appreciated.

Running windows server 2016 IIS v10.

Thank you.