Did you try to re-pair them? If it won't help, reset them first and re-pair. http://www.tp-link.com/en/faq-601.html http://www.tp-link.com/en/faq-258.html

vizer wrote OK, just installed latest firmware, set all back and what a disappointment, now is signal at 2.4 GHz even worse, in average 2 - 4 % lower !! Still don't have answer how many upnp ports...

If it is quite urgent for you to solve it, you should submit a ticket or call TP-LINK support team directly instead of complaining here and asking for a solution....

I see... Do you still want to buy a dual band router like C7 or just a single band router like TL-WR841ND? :)

What's the operating system of your PC? Did you install the driver? http://www.tp-link.com/en/faq-284.html

Do you have any wireless clients which will work with 5GHz band? If not, it is not nessary to buy a dual band router as your ISP speed is 4mbps. How did you confirm that Wi-Fi problem is caused by...