Have you checked the duplex/speed status of your port ?
Try taking the cable from one of the faster PCs and connecting it to the slower PC.
If you swap port does it make a difference ?
Have you upgraded the network card drivers on the slow PC ?
Yes I updated the drivers and tried another pci card with new drivers . I used the same port and cable to connect to the slow pc as was used on another 1 .where from here ?