I don't know if you know so I will start this anyway, your internet cable and internet port are called an Ethernet cable and Ethernet port in the I.T. A world so when I say Ethernet cable or Ethernet port you should know what I mean.
1. Check that the Ethernet cable is plugged into your laptop and that it's plugged into the router/modem you are using, (I know you said you checked it but it's good to check it once more)
2a. Then vary that both indicator lights are on the laptop Ethernet port
2b. If the lights are on, then look at your router/modem and see if the Activity light is on, on a router you're looking for the number flashing which represents your Ethernet cable, on a modem look for a light marked Activity or LAN usually it should flash amber/orange.
2c. The amber/orange light on the laptop Ethernet port and the modem should be flashing which would indicate network activity; on the router the number would be flashing which indicated activity.
If they are on then you can skip step 3 and go to step 4 but I would recommend doing step 3 just to be safe
3a. If you have another PC or laptop plug the Ethernet cable in it and see if you are getting the same issue.
3b. If the lights are on in step 2 and the indicator lights are flashing, and if you have tried 3a with the same result then try replacing the Ethernet cable first and repeating the first three steps before doing the rest.
If you are still experiencing the problem then continue on.
Any website listed below please download the software on whatever computer you are currently using and run then use them on your laptop when asked for.
4a. Go to this website http://www.majorgeeks.com/files/details/winsock_xp_fix.html and the download WinSock Xp Fix
4b. Run the tool on your laptop and first choose Reg-Backup and save this backup in some place you will remember, this is to ensure you can undo any changes that were made in the event a problem arises.
4c. Then click Fix and click OK on the prompts that come up, your laptop will be restarted once finished.
5. If it still doesn't work then:
First go to http://us.acer.com/ac/en/US/content/ask-acer/acer%20lan%20driver;-;-;-;- choose the correct version of your OS and download the LAN Drivers to a place you will remember you may need them later. After downloading, then continue with the steps below:
i. Right click My Computer Icon
ii. Click Properties
iii. On the box that comes up click the Hardware Tab
iv. Click the button marked Device Manager
6. Once in Device Manager look for the Network Adapter
i. Click the plus icon next to it too, that shows your adapters
ii. Next Right click your adapter and choose to uninstall it
iii. After uninstalling the adapter close the Device Manager and the Properties box for My Computer
iv. Restart your laptop.
7. Once the system restarts windows should auto detect the Ethernet port and reinstall the drivers that came with the system.
8. If it did then perform step 1 and 2 again, and vary that the network cable unplugged message is no longer there.
9. If you still have the same problem or if the drivers didn't install try installing the drivers you download before and perform steps 1 and 2 again, and vary that the network cable unplugged message is no longer there.
10a. If all when well and the message doesn't there open a browser and see if any pages load.
10b. If it didn't go well and you are still getting the network cable unplugged message then I would assume that your port has gone bad.
10c. If this is the case you can buy an Ethernet USB adapter that would allow you to get online using your Ethernet cable.