Third access point ... does not go either!

Third access point that I do change within a year.
The first two were the D-LINK, now that I have the Linksys ..... but this also gives me problems.
It connects every now and often have to unplug its power supply, wait a couple of minutes, hang up the match and then magically goes. Incidentally, I noticed that can connect two computers, the third sees the network but can not connect, then who arrives first at home you connect.
In the past days did not work even with this "trick" it connects for 3 seconds, and then for two more hours went.
I tried to change the channel, both with this and with other .... but no, I have always problems.
I tried to take away for a while the cordless close because I could do interference, but nothing .... always the same problem also note that at home we have only simple TV and PC, then nothing antennas or decoder type sky that maybe can do interference.

What the hell is this?
There is something around my house that problems?

You know me?

Sorry for the outburst

The access point is connected to a router? The router has the dhcp open? If you distribute those IP? EPA and the dhcp off (must be switched off)? You set the data rate?

I have no idea about the most of the things
The access point is connected to the power of fastweb and current, and we should connect 4 pc.
How do I know the information that you asked me? Where should I look?