Sprogs,
I'm glad you solved your problem.
If you had not, I would have been very suspicious of the Belkin box itself - and of how it might have been treated by that retailer.
Over the years, I have had 3 different modem/routers -
1st. Netgear - just didn't work. Took 2 "new" boxes before one would work.
2nd. Belkin. Some intermittent fault. Took it in to work IT who fixed it, but as they put it............."We have no idea why"
It worked brilliantly for some time after that. It's only gone in to my storage space due to BT giving free "n"s.
3rd. BT "n". Now on 2nd of my BT black "n" boxes. The first just stopped working every now and then. Quite random and impossible to diagnose. After about 5 * 1 hour calls to the BT "help" line, they sent out a Broadband engineer, who said "Oh, I've never seen that before" (A real Mandy Rice Davies sort of comment). New box in and appears to be working.
As we don't buy these boxes very often, (it's hardly a routine repeat purchase), I do wonder how many either come with a fault, or get thrown around by store staff/delivery folk, and therefore just do not work when we get them home.???