1 you can try to factory reset and reconfigure the modem
2 change the channel
3 how many client devices are there connected to the modem?
4 what kind of device do you use for WDS or universal repeater?

First of all thank you so much joyce for your interest to help,

I already did factory reset many times and even reinstalled the modem firmware and reconfigured it from scratch, but the problems still exist.
Today I changed the channel - with inSSIDer software help - to choose less overlapping channel.. and so far it seems to work fine.

I have a home network with three desktops connected via Ethernet cables and 6 devices via wireless.
I'm using TL-WA701ND V2 access point to extend signal to my brother apartment as the router signal is not strong enough to reach there!!!!!!!!!!!!!, I tried WDS but every time I start using it; it causes problems with router and the connection drops so frequently (I knew later that TL-WA701ND V2 already has problems and many people complain about its stability..... How lucky I am..!!!). So, I took it away for this time till solving router problems and I'm using now my old Thomson router as an access point via wire.

Now in addition to dhcp and wireless problems I noticed that internet connection also drops from time to time, below you can find a screen shot for system log:





I also contacted TP-Link Vendor here in Egypt and he told me that he already contacted TP-Link concerning these problems and they reply there will be a new firmware soon to solve it... I hope that anyone here confirm this please!

I contacted TP-Link support 5 days ago using this form http://www.tp-link.com/en/support/contact/ but I didn't get answer till now :mad:

Update: Still have wireless problem even after changing channel. my wireless connection drops down for about 20 to 30 seconds and then back alive again!!!!!!

Try disabling the 2 firewall settings in the Advanced setup tab, under Firewall. Save and Reboot. At least, It worked for me :)