Have you just applied an update? To what?
When it stops you actually lose link? No LEDs on LAN1 on the 4100?
Can it be restored simply by unplugging and reconnecting the link cable without clearing the DHCP leases?
The DHCP server shouldn't make any difference to a NIC link like that.
What do you see logged when you get back in?
What link speed does it usually connect at? Is the link to the switch via a long cable?
I would guess this is a link negotiation issue with the switch in some way.
Steve