Are your network interface config files gone now? Or perhaps the problem is the new kernel does not have the NIC module(s) built for it that your old kernel had? I have to custom build/install the network modules for my NF7-S motherboard each time change to a new kernel because they are not intergrated into the kernel I am loading. Fortunately this isn't difficult to do as I don't have to configure/rebuild the new kernel ( which I suck at ), but it is irritating.
You can type "/sbin/lsmod" to get a list of loaded modules and see if the one(s) for your network card are loaded.
Other than that idea I don't have any more help to offer.