Some have had similar problems when the router is set to "repeater mode" in their settings, especially when range extenders or secondary routers are used.. Check your settings and disable it. Are all settings at default on the router?
In addition, make sure you have the latest firmware for your router.
Unfortunately, you've told us nothing about the computers which are connected.. Operating systems, make and models, etc.. To test things, have you disabled the firewall on the router to make sure access is correct? If any XP computers are being used, make sure that have Service Pack 3, plus all updates installed...
Hope this helps.
I have some weird problem with my internet connection.
I have a modem adsl which is connected to wireless router (Edimax).
I have a PC which is connected directly to the router and I have a laptop and some smartphone which uses the wifi.
My problem is that the wifi working only when the pc which connected directly to the router is on.
Is anyone have a clue/hint/suggestion why the wireless internet works only when the PC is on?