What Browser are you using?
Try a different browser and see if it does the same thing?
Any 3rd party firewall programs installed?
What OS are you using?
Additional tips
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?
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 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 on each radio?
What security mode are you using? WEP, WPA or WPA2? Preferred is WPA2 and Cipher type to AES only if your device support this.