flashing DSL light - initialising - sounds like lack of sync.
You say you've used it before - same connection different ISP or ??
yes i used the router its self for 9 months on my old ISP (the ISP that gave me the router) so it was a diff connection but it worked none the less
just to confirm its not locked down with custom firmware like for example a BT home hub or anything like that so its not the firmware stopping it from connecting to a diff provider it just has the generic firmware zyxel ship with the router, all they did when i was with the was to block admin access and only give you limited access to not mess with things they did not want you messing with but when i left them they gave me access to the full account (called supervisor its above admin) so i could use it with plusnet
the only difference is my old ISP did not use PPPoE i think it was something like IPOE and used VLAN 10 to connect but ive factory reset it and started new and obviously using PPPoE for plus net.
the router its self has a fair few settings so all i can think of is im doing something wrong within the settings which is why its not working
at the min im using a OR modem and a unlocked HH3 the router PN supply is terrible, but seen as i own this zyxel im wanting to use it for the all in one box experience, the fact it has Gbit lan and also the wifi is actually very good it can still connect about 5 houses up even on a phone, were as the HH even though its better than the PN wireless its still not exactly brilliant