A couple of days ago I added an old router as an access point as a test for future use, and all seemed to work fine.  I did not leave the access point connected as I was only doing tests for the time when I will need it to extend the range of my wifi for an event coming up.  However today the various devices logged in to the TP-Link router gradually went off one by one, and despite putting in the correct password they are all unable to log back in.  I can get access to the internet by putting the old router back in line and logging into that - it is getting the relevant IP address for each device from the TP-Link, but the devices don't seem to be able to get it direct from TP-link.

I'n no expert (in fact a beginner!) so I don't know where to start looking for an issue.  I think the only thing I changed in the TP-Link setup was to add the ip address of the old router and make that a static IP.  The other setting up I did was in the old router, so if that isn't in line I wouldn't have thought that should make a difference.

Any assistance to sort this out would be appreciated. 

Thanks

Jan