To log on the DAP-1522 menu, if you are connected via cable, you must know the IP address of the DAP-1522 (the default should be 192.168.0.50) and the PC from which you are connecting must have an IP address from the same subnet (for example 192.168.0.51).
Sometimes I loose the (wireless) connection with my DAP-1522 (I still don't know why) and I have to restart my router to re-establish it.
If you want to access the DAP-1522 via wireless and you think that it is working correctly, to find the IP address you could also log into you router and see if it is listed somewhere (wireless clients list, DHCP leases, ...), or you could find it with some network discovery software.
If your DAP-1522 has an old firmware, you should consider updating it to the latest version (be aware that version 1.21 will not work correctly with Firefox browser, the wireless network settings menu will be missing), maybe the issue you are experiencing was resolved with a new firmware.
For the connection drop issue, you should also try to move the DAP-1522 do a different position or change the orientation, or change the wireless channel used in your router, sometimes that can help improve the signal strength. Sometimes.