ADO.NET App Stops Trying To Reach SQL DB

We have an ASP.NET app on our internet server (IIS 6) that displays data (company news headlines, etc) from a SQL Server behind our firewall, using the SQLClient objects.

Several times now we've had a situation where the SQL Server became unavailable for a length of time, once when we upgraded hardware, and again last weekend when power to the whole building was down for 18 hours. Even after the SQL box came back up, the headlines did not show up, and setting it to display the error told us it was getting "SQL Server not found or access denied" errors. We still have older, regular ASP pages on this same IIS server that also access the same SQL Server, and they were getting their data with no problems. We tried restarting the IIS server, but it did not resolve the problem. The solution was to reboot the internet server box.

So, why did the .NET app give up trying to reach the SQL box? Is there something else we can reset, other than rebooting the IIS server?