As I know, System blinking is normal, which means the device is working properly. Not sure what's the problem indeed.

Burty, IP address of TL-WR740N can be 192.168.1.1 or 192.168.0.1. If both of them are not working, check default gateway of your network connection.

Try a different USB port. From user guide, if LED is on, the driver has not been installed. Right click on Computer, go to Manage--Device Manager, and double click on TP-LINK adapter. Make sure it is...

Hi Leo, if ping test is OK, it means connection between AP and PC is OK. Open Start menu, in search box, type in http://192.168.1.254(ap's IP) and press enter to see if you can open it properly.

http://forum.tp-link.com/showthread.php?1608-Beta-firmware-Solved-TL-WR1043ND-hang-up-with-high-bandwith-and-WEB-interface-dies&region=china This post is collecting such cases. I think you should try...

Configure WDS on TL-WDR3600 for a try. Your device can be connected to 3600 either wired or wirelessly. This will be helpful. http://www.tp-link.com/en/article/?faqid=440