I don't understand "the internet was working fine, and I didn't think to check the internet connection". How do you know it was working fine if you did not check it?
With the virtual machine not running, check its network settings in the VirtualBox configuration window. Sometimes they change spontaneously -- I swear they do!
If you don't see anything amiss then post the output of
VBoxManage showvminfo <name> | grep NIC
where name is the name of your virtual machine; this is case-sensitive.
Please also post the output, from the Windows system, of