More information needed:
Wired or wireless network? Is the laptop connected directly to the router or some interim device: Wall outlet, powerline adapter, switch, access point....
If wired, have you tried another known working ethernet cable?
How many devices are on the network?
Are other network devices experiencing network connection problems?
One immediate thing you can check is to ensure that only one network adapter (either wired or wireless) is enabled.
Not both adapters at the same time.
Look in Reliability History on the laptop. There may be some error codes or warnings being captured with respect to the loss of internet access.