Question : Wired, can't ping only if I clear arp table

I have a linux box that I can't ping it or connect to the internet from it.
Only if I go to the router and clear arp table then I can connect to the net and ping it from other network. After around 10 minuts or less it goes back to the prevous status: can't ping and can't connect to the internet, I can still connect to it from the same subnet. but not from another network (vpn tunnel).
Any ideas of what would cause this problem?
is it the nic?
a hardware problem?
a software problem?
Router problem?

------- All other computers in the same subnet connected fine and can ping from or to other network except this-------

to see a detail of the problems and outputs see the first part of my question here that led me to clear arp table to make it work temporarly:
http://www.experts-exchange.com/Operating_Systems/Linux/Q_21757373.html
thanks for your time

Answer : Wired, can't ping only if I clear arp table

If the switch is a managed switch you may want to look at it to see if there anything unusual there.  Is there just the one switch between you and the router?