What HW version is your router?
What FW version is currently loaded?
What ISP Service do you have? Cable or DSL?
What ISP Modem do you have? Stand Alone or built in router?
What ISP Modem make and model do you have?
If this modem has a built in router, it's best to bridge the modem. Having 2 routers on the same line can cause connection problems.
Ensure DNS IP addresses are being filled in under Setup/Internet/Manual?
Turn off QoS options.
Turn off Advanced DNS Services if you have this option under Setup/Internet/Manual.
Turn on DNS Relay under Setup/Networking.
Setup DHCP reserved IP addresses for all devices on the router.
Ensure devices are set to auto obtain an IP address.
Set Firewall settings to Endpoint Independent for TCP and UDP.
What wireless modes are you using?
Try single mode G or mixed G and N?
What security mode are you using? WEP, WPA or WPA2? Preferred is WPA-Personal. WPA2/Auto TPIK and AES.
What wireless devices do you have connected?
Any cordless house phones?
Any other WiFi routers in the area?
Turn off all anti virus and firewall programs on PC while testing.
Turn off all devices accept for one wired PC while testing.
I have the exact same problem and it is annoying. Everything stays connected and I'm unable to open new web pages. It happens at least twice a day now and this happens on every computer (11 of them) and our 4 mobile device . I tried dhcp release/renew, ipconfig dns flush, tried opendns and still no good, and advance dns is already disabled. The only thing that seems to work is a reboot or to power cycle the router. Also, if you do nothing and wait about 10-15 minutes it will work again if you don't want to kick anyone off their games. I had it for almost 4 months and it happen just a month ago. At this point I'm just going to get a new router.