What level of wireless security encryption are you using?
Maybe try experimenting, change from WEP to WPA (personal) or WPA2 if support by all devices) change from TKIP to AES if all devices support it. Maybe even run it open for a brief period, just to see if your issue persists.
What channel are you using, ususally defaults to 6, maybe experiment and change it to 9 or 11 depending on options available.
Not familiar at all with that particular router, but there is probably an option from within the user interface to enable UPnP, so try enabling that and then open the service console (type services.msc into the search or run dialog box) on your computer and scroll down to UPnP Device Host and start it (maybe even set the startup type to Automatic by double clicking it if you want) see if that helps. Also from within the router interface you should be able to select your card/performance type, something like
abg, or bg, or g only, etc., set that to correspond with the card you are using. Also within the router interface there is probably log information which may or may not be helpful in pin pointing the issue.
Finally, entertain the potential for third party program processess, or services that may be causing this issue. You could boot into safemode with networking to see if the problem persists or perhaps use this article on
Clean Booting Windows 7 to see if you can further your trouble shooting efforts.