Thanks Rory,
the dvr is connected via a router with cat5, the pc then is also connected to the router with cat5 .
Ive been into router settings and the dvr and pc show up as attached devices, also when i "ping" it its ok.
The dvr is connected to a tv and when status is selected the ip address and the mac address all tally up.
I think ive narrowed it down to the software but it looks like you have seen most things when it comes to routers.
Its frustrating to say the least, but hey cars still fine.