Problem with D-link DIR-635 - assistance required

[Banshee]

Hello,
some assistance please. I've had a look about and I can't find any mention of the particular problem I'm having. Has anybody seen anything like this? I've upgraded to the Dir-635 and I'm having intermittent problems using wireless networking. Effectively, the router stops transmitting (network doesn't show up in list of wireless networks). A hard reboot of the router doesn't fix the problem i.e I can get back on to the router but there's still no internet access, so I have to power the cable modem off as well. As I said it's a DIR-635 H/W version B1. (I know the firmware is slightly out i.e. 2.20 rather than 2.21, but then I've just discovered that). The router can run for 5-10 days without problems and/or sometimes has the problem every day or two. Has anybody experienced similar problems? Any suggestions? Thanks in advance.