You are getting "169.254" addresses allocated by Windows because, for some reason, the network adapters have been unable to access the DHCP server (the router) to get the correct addresses.
<<< My desktop pc connects to the router via an ethernet cable. When this happens the dhcp server on the router assigns my desktop network card an ip address ?? (which is 192.168.1.2)but if my pc has already assigned that network card an ip address of 169.254.223.249 then there is bound to be conflict ?? >>>
If your desktop PC has what is known as an APIPA address (Automatic Private IP Addressing) - a 169.254.x.x address allocated by Windows - the adapter will continue to seek a DHCP server and, if it finds it, the address will update to the one allocated by DHCP. Your adapters are not finding the router to get the address.
<<< Also what would happen if i just chose the turn off the dhcp server on the router ?? would this cause more problems ?? >>>
Whilst you could disable DHCP in the router and allocate fixed IP addresses to the network adapters, there may be a more fundamental problem that is actually preventing the PCs and router from communicating at all.
<<< The lease on the ip's is 1 day ? is it just a case of increasing the lease time ? >>>
That isn't an issue. The IP address will be renewed before the lease expires, it isn't something you need to think about.
<<< and when i reboot or turn off, will these ip's that the router has assigned change ? or do they stay the same ? >>>
That can vary with different routers. My Belkin used to allocate an IP address to a PC and it always kept that same address. My current router, a Buffalo, allocates IP addresses on a "first come first served" basis, so the address depends which PC is booted first.
To be honest, particularly as you are also having a problem with a "wired" ethernet connection, I would be inclined to reset the router back to factory default settings and start again. Check the manual, but there are normally two reset options - "soft reset" which just reboots the router and "hard reset" which wipes it clean and reverts to the default settings.