Zyxel 660HW DSL LED keeps flashing

Hi, Hopefully, you will be able to assist me with a connection problem. I have been successfuly accessing the Internet etc. via the Ethernet connection on my Speedtouch 536 routerwith no problems at all. Recently, I purchased a Zyxel 660HW ADSL wireless router with the intention of using/sharing the Internet connection wirelessly with my laptop. I installed the Zyxel in accordance with their Quick Setup Guide and after ensuring I'd performed a factory reset. Everything seemed OK with the installation apart from the DSL LED keeps flashing on the unit and doesn't synchronise with my ADSL. Therefore I cannot use it. It does state in the Zyxel literature that after setup and an approximate 2 minute restart, I should have access to the Internet. Incidentally, I did revert back to my original setup (Thomson 536 router) thinking there may have been a temporary problem with my ADSL line but accessed the Internet no problem as before. Do I need to completely remove the Thomson router details from my PC prior to the Zyxel installation perhaps?

Is it possible you can you advise me how to rectify the problem please?