Frequent Connection Drops - IP Conflict

[#1]

Hi,
We moved over to the plusnet service over a year ago, and have always suffered annoying connection drops, but this seems to be getting worse, we have always put it down to what seems like quite a poor router, Thomson TG585 v7. We never had an issue with BT.
The symptoms are connection inexplicably being lost, and then taking 2-3 minutes to go through the process to automatically reconnect to the internet. This is for all devices on the network. At least once a day. Sometimes it seems to be when someone else boots up their computer.
I have wondered if this is due to IP conflicts. I have had the message on my laptop a few times, but going into the router settings I can see that most of the devices share an IP with at least one other, 5 times in one case. Should the router not be handing out unique IP's!? I have checked the DHCP pool, looks ok. We have quite a lot of devices, laptops, phones, games consoles etc.
How do I resolve this situation? I have tried my best, I am compitent in computing but networking issues seems to have its own area of jargon and confusion! I tried IP release / renew in prompt but it wouldnt let me do it. I also tried to put the old router from BT back on, but it will no longer connect to the internet, and I couldnt reset it.
Many thanks for any help!

[#2]

Quote from: M444

The symptoms are connection inexplicably being lost, and then taking 2-3 minutes to go through the process to automatically reconnect to the internet. This is for all devices on the network.

Your devices connect to the router.  The router connects to the internet.  If you simultaneously lose the internet connection on all devices then the router must have lost its connection to the internet.  There is a standard fault-finding procedure to address such problems.

Quote from: M444

I have wondered if this is due to IP conflicts.

No, it isn't.  IP address conflicts usually arise when a device connects to the router then enters a sleep or hibernation state.  After a period of getting no response from the sleeping device, the router assumes it has been disconnected and that the IP address it had is free to be assigned to a new device.  But when the sleeping device wakes up it still thinks it has its original IP address so it may report a conflict if something else has been assigned the same IP address in the meantime. 

Quote from: M444

I also tried to put the old router from BT back on, but it will no longer connect to the internet, and I couldnt reset it.

You would probably need to reflash the firmware for your old router to prevent it being tied to BT.