Try single mode G or N or mixed G and N?
Channel Width set for Auto 20/40Mhz or try 20Mhz only.
Try setting a manual channel to a open or unused channel. 1, 6 or 11. 11 for single mode N if the channel is clear.
Preferred security is WPA-Personal. WPA2/AES Only. Some WiFi adapters don't support AES, so you might want to try TPIK only or Auto.
Any cordless house phones?
Any other WiFi routers in the area? Link> Use
InSSIDer to find out. How many?
Turn off WISH, and WPS under Advanced.
Try turning off Short GI, WLAN Partition,and Extra Wireless Protection if you have it. Under Advanced/Advanced Wireless.
Enable
WMM Enable Under Advanced/Advanced Wireless.
Turn off all anti virus and firewall programs on PC while testing. 3rd party firewalls are not generally needed when using routers as they are effective on blocking malicious inbound traffic.