SIP-T43U causing pc to lose network connection

[itbioveld]

We have recently installed several SIP-T43U phones. We were connecting them by connecting the network cable from a POE wall outlet(switch) to the phone and then connecting the phone cable to the pc. This works for a while - sometimes months - but then the pc starts losing network connection intermittently. The fix has been to connect both the pc and the phone separately to a non -POE switch and then connecting the AC adapter to supply power to the phone. I also tried connecting the pc and the phone separately to a POE switch and found that after a week or two the pc had intermittent network connection loss. The only fix seems to be to install and connect to a non-POE switch and use an AC adapter. However, one of the AC adapters has died and I have no replacement so I have one phone that is not operational. I need a solution so that I can use the phone again with a POE connection.
We would prefer just to use the original(normal) method of connecting the network cable to the phone and then connecting the pc to the phone. Is there something that I can check or configure that will fix this problem? Is there a firmware fix for the phone that will fix the problem? Thanks.