Try using an older version of the Kernel then.
When I searched for "Toshiba C655d-S5200 ubuntu ethernet" on Google, I got
hits from 2011 and 2012. Back then, they recommended a kernel upgrade, or manually installing drivers for the Realtek chipset.
This should give you the chipset number:
lspci | grep -i ethernet
I suggest to start your search from the chipset number: search Google for example for "RTL8188CE ubuntu freezes", see if something useful pops up.